A phrase used to describe many aspects of a game of beer pong - more specifically a game of beer pong in which all of the participants are already thoroughly intoxicated.
It can be shouted to one's teammates to mean beer pong, i forgive you, cheers, or you're my best friend ever.
Hey man, wanna play some phong long?
Aw, shit man, drink up - phong long!
Sorry about that one dude, thought we had it..
No worries man - phong long!
I can't believe we won again man, phong long!