Just thought of another one, if price doesn't matter. Davio's, which calls itself an Italian steakhouse, has very good food and ambience. Popular, lively. It's just a few steps from your hotel. Has a bar.
Some of the places mentioned are BYOB, which is very big in Philadelphia - you bring your own wine, no corkage charge. Matyson is one of our best BYOB's - small, casual.
Matyson is very close to Sofitel. Depending on what part of the week you are in town, they have great weeknight tasting menus. However it might be lacking in the atmosphere department. Pub & Kitchen is a nice upscale pub with very good food and a nice neighborhood feeling also not too far away.
It's perhaps considered a bit passe in these places, but I've never had a bad meal nor bad experience at Friday, Saturday, Sunday. The atmosphere is very cool and they have a great (and exceedingly affordable) wine list.
Continental Midtown is definitely an experience; I'd go there for one of their great/unusual cocktails and a light bite or some desserts.
I was not especially impressed on my one visit to Tinto so far, compared to the many praises for the place here.
There's also the new Sansom St. Oyster House which is getting huge buzz but I haven't been.
On the corner of Sansom and S. 20th (so, three blocks from you), there is Tinto (Basque Tapas). It's excellent. Whiskey Bar next door is open now, so you could have a drink there. And Cappogiro, suggested above, is across the street. Very convenient, but even if they weren't, they are worth going across town for. Noble, a sort of New American place, is down the street too. It's had mixed reviews, but I thought it was very good the two times I have been.
Wherever you have dinner, make sure to get gelato at Capo Giro. The gelato is made fresh with amazing ingredients and flavors. There are two stores close by and almost equidistant from the Sofitel, one at 13th and Sansom, one at 20th and Sansom.
Sofitel used to have an incredible deal, $139 for a weekend night including breakfast for 2 (room service allowed) and (if you're a member of their free loyalty program) 2 free drinks at the bar. Every time I booked it, I thought it must be some kind of mistake. I guess they wised up eventually. sigh...
Alma de Cuba is a block away and has very good ceviche and Latin cuisine. If you are not averse to walking another block, Estia has deliciously fresh fish flown in from the Mediterranean and great grilled octopus. Alma is more "hip" and trendy while Estia is more restrained but not stuffy.
For a quick bite, hit Argan, a immaculately clean hole-in-the wall half a block south from the Sofitel for delicious, cheap Moroccan cuisine including tangy, delicious lamb and roasted eggplant in pita-like bread.
And of course, no Foodie trip to Philly would be complete without a trip to Reading Terminal Market. It's a scenic, safe 10 minute walk from your hotel at 12th and Arch St's (to the northeast from the Sofitel).