Got to love that old end gates for TWA in the background. It was always one of the more unusual gate styles. A single jetway extended out from the end of the terminal. At the end of this jetway, three separate jetways attached forming what would be access for three different aircraft.
If I recall correctly, Spirit actually tried a rather rapid expansion at PHL to complement the Atlantic City operation. After what were probably quick losses by PHL's incumbent carriers, they pulled out of there as fast as they entered.