Assuming it takes you two hours to arrive, clear customs, check bags and get to the rental spot, you'd be leaving JFK at 12:45pm.

JFK-PHL should take about two hours by car. I have done it in less time (but I have a lead foot). You should be in PHL in plenty of time for your flight. You may even have a chance to see a little bit of Philly on your drive in!

In the past, I have tried to price van service and it's about $50 each way.

Best wishes for safe travels.