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scharal. If you do miss your connection due to Customs, and while US is rebooking you on the next flight, ask about a meal voucher. Depending upon the individual reissuing your ticket US may or may not issue a meal voucher. It will only be worth between $7 - $10 and can be used at any food stand in the airport.
I don't know if you found the
PHL Airport link which will provide related info on the various terminals and transiting between terminals.