There are certain effects that make enemies do an immediate attack against a player. If this happens before the combat phase, does the enemy still attack during the combat phase as well? What about if such an ability happens during the combat phase? I've been playing it that they make two attacks, but I was wondering if some rule limited enemies to one attack a turn. I'm guessing not because enemies don't exhaust to attack from what I know. Thanks in advance!

Yes, they attack again. Immediate attacks always happen in addition to a normal attack that would occure.