TheLiam, "phent_addcentralforce" works only with physical object, that doesn't have gravity, or am I wrong?
I'm not gonna add any torque or force to my physical objects.
I just need them to do not move in Y coordinates, if they for example fall from hight place and rebound from the floor or other objects. Simulation needs to look completely as in a 2D game, but with 3D models.

Helghast, do you mean something like this:
///
while(1)
{
phent_enable(my,0);
my.y = 0;
phent_enable(my,1);
wait(1);
}
/////
If not, please, explain a bit more. Thank you all guys, for helping me out.