It you have the full 50 minutes from landing to start of boarding, I'd say you're probably OK.
But it really depends on which terminals, what the % on-time the flight is, and where your seats are on the plane.
PHL is an American hub and most of their flights are in terminals A,B,C - B and C are pretty close, A is also pretty close (but there's an East and West A - with A West being farther away). There are some moving walkways between the terminals, so that helps. If your're not on American (or mixing/matching airlines), and you come in to terminal F, I'd be a little worried, since that's a little more out there (I haven't been in that terminal in many years, so I can't really tell you how long you'd need).
The PHL airport isn't all that big though.
I'd suspect there's a good chance you'll be ok you're taking American for both legs, and you snag seats towards the front of the plan. Assuming the first leg isn't running late.
Problem I have with connections is you're in trouble if the first plane is late, and that seems to happen a lot these days. Taking an morning flight helps.