Well, it's certainly an artificial environment of some sort.
It doesn't use construction or engineering techniques that we can
understand.
(Unlike Star Trek, where the ships are based around how they would 'really' be built using methods and theories we already know.)
I don't think Time Lord construction can be quantified.
It might be more like a computer program. Like a holodeck, almost.
Many stories imply that the interior is calculated using mathematical equations.
Like a computer program. Lots of little 1s and 0s.
In some stories, the defined mass of the TARDIS can be reconfigured from its own central computer, and whole sections can be 'jettisoned' (whereby they simply disappear, it isn't like it loses actual physical parts in the process it's more like they just gets put in the equivalent of the desktop 'recycle bin' which is then emptied, whoosh gone, and the computer then recalculates the total 'mass' of the vessel based on how many percent of it has been jettisoned).
The Doctor 'loses' the zero room and the TARDIS pool this way.
The whole thing with changing the TARDIS control room 'wallpaper', as inferred by the changes throughout classic Who and confirmed on-screen in the new one, also seems to tally with the TARDIS at least using
some kind of artificial projection technology to create its interior environment.
Original Who called this 'Block Transfer Computation'.
But on the other hand, there are stories where the Doctor tinkers with actual electronics. Where he opens up a roundel on the wall or a panel on the console, and uses his sonic screwdriver to actually fix something on a circuit board or bond some wires together or whatever.
Early (1960s) stories erred more closely to this.
The very first Dalek story makes mention of fluid links, and other stories (even up into the 1980s, after the above mentioned 'Block Transfer Computation' technique had already been established) act like it uses adaptors and parts that need replacing.
In at least one story the TARDIS actually runs out of gas (or the galactic equivalent, Zeiton Ore) and the Doctor is just like, "Well shit, we're stuck here now aren't we?"
"Arc of Infinity" shows us one of Gallifrey's mechanical engineers, Damon, whose job it is to give TARDISes refits in his workshop.
It's basically said that the TARDIS is pretty much like a car, or any other conventional sci-fi spaceship for that matter, and that by rights the Doctor
should be taking his TARDIS back to Gallifrey for a check-up every few millennia to keep it operating at peak efficiency.
Further to this, the new series originally based its 'downbeat' TARDIS interior on the premise that without Time Lord maintenance crews to help him out, the TARDIS has effectively been patched up with Do It Yourself bodge-jobs by the Doctor using whatever has come to hand over the centuries (hence why one of the levers is the air-pump for a bicycle).
So there's definitely
something of the ship which is made up traditional components, actual physical parts that get old and need fixing or replacing.
So the only conclusion I think we can draw is that the nature of the TARDIS' engineering is
somewhere in the middle. It's the only fair way to marry the two above positions together.

That there's obviously some kind of basic unseen physical "core" to the craft, possibly only based around the central console itself, from which elaborate computer programs "project" an infinite, but still broadly defined, artificial sense of space using complex mathematical equations. A TARDIS
without any of these things working is probably just a tiny room with a console, lots of technical doo-dads, and not much else.