Paul's Philadelphia Eatery was on Senate Street in the Vista, in the same building as 5 Guys and The Flying Saucer, right next to the former Alan Ray's Salon, and on the same block as the former Damon's.
Once you get past "Philly Chese-steak", my knowledge of Philly cuisine is a bit thin, and although I do get to Very's on Two Notch once or twice a month, I never managed to make it to Paul's.
I suspect the environment for restaurants in this part of the Vista is a bit mixed. It's not Gervais Street, so you're not going to get the casual passers-by. 5 Guys does well, because people specifically go looking for a 5 Guys.
(Hat tip to commenter Badger)