Originally Posted by
swag
While I have no experience at PHL, I frequently use the "wrong" checkpoint at other airside-connected airports, and have never been turned away. If ever questioned, I'll just say that I prefer the restaurants near the checkpoint I'm using.
Or you can say that the line at your airline's terminal was huge, this terminal's line was much shorter and you didn't want to miss your flight on account of the very long line.