I recently took this route (on an award ticket)
not terrible flight & service ok,
you need to check in at he us airways counter in LGA,[gotta show passports] IMO this might be an issue if they are crowded, also give yourself enough time to make the connection in PHL [my flight from lga to phl was delayed an few hours ]
as it is an international flight you need to clear security in both airports,
Cant comment on the return flight and poing through customs on the way back