What time are you coming in? If it's the daytime during the work week, go to Mikey D's Grill, a street cart, at 33rd & Market:
I don't know exactly when he leaves, most of these guys are gone by 3:00 or 3:30.
If you're coming outside of work hours, there really isn't anything super close. Abner's at 38th & Chestnut makes a pretty good steak, it's about a mile away. If you don't want to walk, you could take a cab or subway/trolley there quickly and easily.
Abner's is a pretty classic steak. Very similar to Jim's of 4th and South (I think they share some common lineage as far as owners.) Truth be told, you can get a DECENT steak at just about any bar or diner in the city. Same goes for lunch trucks.
If it's a nice day, though, Abner's is a short walk.