v. Simply pieced together, the onomatopoeic word phap (also spelled fap, that is used to describe the sound made during masturbation) is spliced with the word poop, meaning simply: To masturbate while defecating.
Brian: Oh man bro, I phoop so often that my bathroom consistently smells of dump and cum.
When you have to crap really bad so you rush to the shitter and sit for a couple of minutes and then you just fart nothing comes out but air and it echos across the whole bathroom.
Did you just hear that?
Yea, I think he just phooped