We usually fly out of PHL early on a Sat. morning (one of first flights of day) and we have never had a line at security (6 trips, all post 9/11). Our last trip we flew out of PHL on a Friday, hit security around noon and were through in under 5 minutes. So, we have never experienced any security lines at PHL, but we usually fly on a Saturday, early, and on non-holiday times. I would think 2 hours is plenty of time.