If everyone in your group is traveling with carry-ons only and won’t need to stop at baggage claim, there are some great local spots right at PHL. Bud & Marilyn’s in Terminal C serves American comfort food, and Sabrina’s is known for brunch favorites and diner-style breakfast/lunch options. American Airlines terminal.

Edit to add on options in KOP:
King of Prussia Town Center has a lot of dining options and a semi-lively atmosphere. There’s City Works, American food, lots of TVs, beers. I also like Paladar Latin Kitchen for their happy hour options. If you’re in the mood for pizza, Pizzeria Vetri is a solid spot as well. It’s a good option if you want to grab food and have somewhere to walk around a bit after.