Found out what PHD Flopper does by experience

[Illmatic]

So the PHD Flopper is a Bomb type of perk, you have to Dive From somewhere with height difference like from Stairs for example and when you dive on the floor an explosion around you will kill any zombies in its radius. it can become very useful at times

[Suhn-Sol-Jashin]

Hold a grenade in your hand while you have that perk and let it explode. XD