Is Philadelphia part of the Midwest or the East coast ?

Middle Atlantic, actually.

It's part of the Northeast.  It's not technically on the coast, but it is very much on the far eastern side of the country, so you could say that it's on the east coast depending on how you define that.  It's nowhere near the midwest...

Philly is a decided part of the Northeast/East Coast.

East Coast, as it's on the river that leads down to Delaware Bay + it's on the East side of the Appalachian Mountain Range

West coast  because it is in massauchtst 

Philadelphia is on the East Coast.

Philadelphia is part of the East Coast. It's a short distance from the Atlantic Coast.

The east coast.

City of Philadelphia, Pennsylvania, USA

The fifth-largest city in the United States and the second-largest on the East Coast,

The Midwest, as defined by the federal government, comprises the states of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.