I assume you mean PHL - Philadelphia International, rather than PHI, which is in Northern Brazil?

I don't have vast experience of PHL, but yes, you have to collect and re-check bags when transferring domestically from an international arrival at (every?) US airport. In most larger facilities, this amounts to pulling your bags off the carousel and walking them through customs and dropping them back off at a bag re-check point before exiting landside to re-clear security again.

At SFO US and AA are still in different terminals. The AA Admirals Club lounge at T2 is very nice, but if you're on US metal, you'll be flying from T1 which doesn't have an Admirals Club, or a former US Airways lounge unfortunately. There is no airside access between T1 and T2 (though there will be in the future).