This question popped up a couple months ago in the Mid-Atlantic forum (Is PHL a 24 Hour Airport?) There was no definitive answer but I'm sticking with my response of "no, you'll probably get kicked out". You're probably free to join the homeless and other connecting passengers landside.

Depending on your flight schedules, if you stayed at the airport Marriott (which is connected to terminal B and you can walk to it), you might actually get 3 hours of sleep.