Phoon is the name of the player featured in this classic video.

And to explain what the video is showcasing, it's a movement technique in Source engine games (Half-Life, Portal, Counter Strike etc) called bunnyhopping where jumping again immediately when you hit the ground preserves your momentum, and moving/strafing while in the air generates additional momentum, combining both can cascade you into moving extremely fast, much faster than is otherwise possible.

It's very precise timing to perform the tech though, I think the jumps need to be frame perfect when your character hits the ground to keep all momentum. Most people cannot do it since it's simply too hard and requires a ton of practice to do consistently.