When you arrive PHL, you will go through US Immigration/Passport Control, claim your baggage and then go through US Customs. After clearing customs, follow the signs for connecting flights and there is a special desk, just outside of customs, to recheck bags. All of this is inside the terminal...you won't be going curbside. After you recheck your bags, you proceed to the security checkpoint (a short walk, all inside) and head into the gate area and proceed to your next departure gate. Barring delays, it should be sufficient time.