If gases turn to liquids under great amounts of pressure, what is a black hole?
The kind of pressures you're talking about with a black hole are well out of the ordinary so what may be a common phenomena with substances doesn't apply.
A cavity in the universe, which nothing can escape.
It's more of a gravity pull then it is pressure
Nobody really knows what form matter inside a black hole actually has - or if it is at all still matter as we know it. And it won't be easy to find out, I guess.
Natures laws as we understand them break down at the center of a black hole, from there we go to quantum physics, where even gravity has no effect. What's going on there are only theories.