(Renamed “Lazarus” from “Phantom” by Kruger; see below.)

The Lazarus went through at least four names…

It was Hans Maximillian Kruger's first ship, which he “inherited” by being its sole survivor after a fight with three Kilrathi frigates; –which ended when the Phantom jumped to another system; but not before a missile exploded close enough to breach the hull, letting the air escape, and killing its captain, Kevin Milady, and gunners Marilyn Langer and Igor. Hans renamed the ship “Lazarus”. It is a cargo ship of unnamed class, capable of carrying 20 tons. Hans had it heavily modified.

In 2634, Winston Turner, Vance Richards and (young ensign) Geoffrey Tolwyn are sent by Admiral Spencer "Skip" Banbridge to the Landreich, for a vaguely specified trip to Gar's Emporium. They take the trip from Hell Hole aboard the Lazarus, having made a contract with Hans.

After their return to Hell Hole, President Blucher drafts Kruger into the FRLS to defend the Landreich from imminent Kilrathi invasion. Turner, Richards and Tolwyn borrow the Lazarus for a trip to McAuliffe, carrying with them the "Lost War Orders"; and then again they leave McAuliffe on the Lazarus to reach the TCS Concordia.

The class of the Phantom/Lazarus is never stated. However, there's quite a few details said about it that allows us to rule out some known ship classes, while at the same time gaining an overall picture of this bird.

From early in the story in Action Stations, we know that the Phantom has a top laser turret (manned by Igor), and a rear turret, twin mass drivers, womanned by Marilyn Langer. Hans Kruger's job is not too clear. At one point, Captain Milady, during an engagement, gets angry at Kruger, saying he could have gotten a bogie that Kruger could not see; so he definitely has some kind of weapon controls; but one might rush to the wrong conclusion that hans is sitting at a bottom turret. This can't be so, because Kruger only has to turn around to see Marilyn (and he's been checking her out, in fact). Hans is sitting at the co-pilot's seat.

And the weapons Hans is in control of are the forward guns. We know this also from the sentence that follows Captain Milady's angry snap:

The fact that there is a rear turret tells us that this is not a Galaxy like we see in Privateer; –the Galaxy class fast transport has top- and bottom-, but no rear-turret (and can't even accommodate a rear turret, as the cargo hatch and docking clamps are at the back. And the fact that the rear turret is visible at the end of a corridor directly from the pilot's seat in the bridge/cockpit, and the fact that Kruger can appreciate Marilyn's beauty without using binoculars, tells us that the distance from the front of the cockpit to the back of the ship can't be too great.

We also know that the top turret is directly on top of the pilot's chair, because Hans has been suffering a rain of tobacco spits from Igor since coming aboard in Gainer's World.

The Lazarus is a lot smaller than a Drayman, as it manages to fly into and land on the Concordia's flight deck. We know also that it has vertical stabilizers at the back, –or else I can't imagine what would be meant by “tail”… In fact, its landing on the Concordia was a delicate maneuver as the top to bottom height of the rear stabilizers spanned the entire height of the deck minus a couple of feet.

Now, the height of Concordia's deck is 42.7 meters (measured from the original model of the Concordia after scaling the model so that its length is 983.7 units). That's like a 10- or 11-story building. Seems like quite a tail, though still quite smaller than a Drayman. But I'd be inclined to think this is the result of carelessness on the part of Forstchen, however, as when the Lazarus is taking off from Johnson Island, Vance Richards wonders if it was wise to take on a dozen airmen as passengers, given the difficulties during take-off. Their weight would be insignificant to a ship so large that its vertical stabilizer is as high as a 10-story building.
We also know that the Lazarus is an atmospheric capable craft, which flies down to land on an air-strip and, as the dramatic take-off at McAuliffe leaves no room for doubt, requires enough forward speed during runway takeoff to make itself air-born without stalling.

In other words, it relies on standard airplane aerodynamic wing lift to become airborne. And to go from ground to orbit, it needs to break the sound barrier many times over, so we're talking about something the likes of an SR-71 overall shape, but shorter. Why shorter? Because the rear gunner position can't be too far away.

These constraints are not easy to reconcile: It's a cargo ship, capable of transporting 20 tons, plus enough hydrogen for ramjet propulsion through the atmosphere, accelerating through Mach 30 or Mach 40 to reach orbital speed, plus having to carry fuel for its ion engines in space. So it's larger than an SR-71 in overall volume; and the height of its tail seems to reaffirm this is a pretty large ship. And it's a hypersonic craft, which often equates to being relatively small in frontal cross-section but long. And yet, the forward cockpit can't be too far away from the back of the ship. Contradiction? Not necessarily… The cockpit could be at the back of the ship, rather than at the forward end; or else it could be inside the ship, and use cameras and displays for piloting and targetting…

As a matter of fact, there's technically never a mention of any “windows”…

Of course, “viewport” could mean “window”, but chances are that if “window” had been meant, the term “window” would have been used. The accident of hitting his helmet on the “viewport” is not unlike when one is using a microscope, out of miscalculation, banging one's eyballs on the eyepieces… This “viewport” is something Kruger has to “look into”; something that produces some kind of 3D view with exaggerated perspective, such as stereovision from cameras set wide appart, making the external view appear small, perhaps; or, in any case, something that produces some kind of visual disorientation, leading to a miscalculation that causes him to bang his helmet on it. Could be some kind of electronic display, or even a mere optical conduit of sorts; but likely NOT a “window”.

Later we read…

…which again seems to point out to there being no windows, as Hans seems to draw all his conclusions from the nav screen.

Before the trip to Gar's Emporium, Hans says to Turner that, among other things, he got the titanium pressure hull laminated with 1/2 inch durasteel. This tells us that the outer armor is removable; which is something we ought to have suspected all along, as the very essence of the concept of “armor” implies easily replaceable protection for some less easily replaceable interior. Pressure hulls are probably welded together into a single piece, which is very time-consuming and costly to repair; and therefore is covered with easier to replace armor panels.

I'm going to ignore the 40-meter tall “tail”, which would make this bird too big; and I'm going to ignore the weight of passengers passage, as it would make it too small. I'll try, instead, to work out the dimensions from the most clearly expressed, intentional data; –namely, the fact that it can haul 20 tons.
What atmospheric capable space ship do we know of that can haul 20 tons? No need to look through long lists; NASA's Space Shuttle supposedly can haul 22.7 tons.
Unlike the Space Shuttle, however, the Lazarus uses no booster rockets to take it out of the atmosphere, which means that it possesses ram-jets or something equivalent for atmospheric propulsion. It also possesses ion engines for propulsion in space, a nuclear power plant of some sort to power the ion engines, a tanks to keep fuel for the ion engines and the power plant, plus jump drive. It would not surprise me at all if it were much larger than the Shuttle.
The Shuttle is 58 meters long, and the fuselage is 8.7 meters in diameter. If it were a perfect cylinder, pi r² * l = 3448 m³ of displacement, but considering that the nose is a bit of a cone, a rough guess would be about 3000 cubic meters. The main liquid fuel booster is a lot larger: about twice the diameter and at least 25% longer, so about four times the cross section times 1.25 = about 5 times the displacement, or 15,000 cubic meters. The solid booster rockets probably add about another 2000 cubic meters. Grand total is roughly 20,000 cubic meters. I'll use this as our displacement for the Lazarus.
In WC, most ships that are atmospheric capable are somewhat squat, rather than cylindrical. Let's assume the width to be about twice the height, and for the length to keep same ratio to the width as the Shuttle's length keeps to its diameter. 58.2/8.7=6.7, so L = 6.7*W and W=2*H, and L*W*H=20,000…
In other words 13.4*H*2*H*H=20,000 therefore H³=20,000/26.8=746.3 therefore H=cubic root of 746.3…
So, assuming the fuselage to be a rectangular box, we get… H = 9 m
W = 18 m
L = 121 m
But since the nose needs to taper to a point for aerodynamics, we end up with a length of about 150 meters.

All of which means that the Lazarus is significantly larger than a Venture corvette, making it the largest atmospheric capable ship in the Wing Commander Universe as we know it. But considering the overall lack of realism in WC ship stats, we could consider making the Lazarus a lot smaller; perhaps roughly the same size as a Venture.