You cannot directly set x,y,z,pan,tilt,roll to an entity set in the physics engine. If you want to change these paremeters, you would have to temporary disable the entity from the physics engine, then re-enable it once your done. Example:

phent_enable (my,0); //temporary disable
vec_set(my.x, temp.x);
my.tilt += 180;
my.pan += 180;
phent_enable (my,1); //enable