Ghost types are immune to it. No damage is dealt.
This is because Flying Press is a Fighting move, which means when it is used on a Ghost the game doesn't calculate the damage because the Ghost Pokemon is immune to it. Since dealing Flying type damage is the move's side effect, it cannot take place since the damage was never calculated. It's like Power-Up Punch. Since the damage was never done and the Ghost is immune to the attack, you don't get the Attack boost.