This portion from this thread usually proves reliable...

US in PHL
US operates flights out of terminals A-West and A-East, B, C and F.

- Most flights in A-West and A-East are transatlantic (TATL) but there will be mainline domestic arrivals/departures and Republic regional flights.
- B and C are mainline domestic, Caribbean, and Canadian flights and also include E-170/E175 flights.
- F is for regional flights (RJs, turboprops) both domestic and Canadian.

Flight numbers 3100-3499 will park at A/B/andC. They are operated by Republic Airlines. NO other Express carrier parks at the A/B or C gates the rest are in F.

Here is the break down of flight numbers
West Side US Airways 0001 - 0699
East Side TATL 0700 - 0799 Also some domestic thru flights
East Side Us Airways 0800 - 2199 Including Shuttle flights
PSA Airlines 2200 - 2599
Mesa Airlines 2600 - 2999
Chautauqua Airlines 3000 - 3099
Republic Airlines 3100 - 3499
Trans States Airlines 3500 - 3550
Air Wisconsin 3551 - 4099
Piedmont Airlines 4100 - 4649
Colgan Air 4650 - 4849

US Airways flight numbers starting after 5000 are code share express flights with United.