Portland is 3 hours behind Philadelphia
Best overlap: 11:00 AM to 6:00 PM in Philadelphia is 8:00 AM to 3:00 PM in Portland.
For the smoothest call, aim inside 11:00 AM to 6:00 PM in Philadelphia, i.e. 8:00 AM to 3:00 PM in Portland. Portland is 3 hours behind Philadelphia, but you'd hardly notice — 7 hours of shared hours makes this feel like working in neighbouring time zones.