Talula's Garden or Vernick Food and Drink for upscale American, Victor Cafe has Italian with opera, Le Virtu is another nice Italian option, Amada for tapas, Zahav for Middle Eastern (hard to get reservation)

Any Stephen Starr place will be good. Parc, as a PP suggested, is a brasserie right on Rittenhouse Square, but a table for 6 might be hard to get unless you’re making a reservation far in advance. If it’s a fancy expense-account dinner and you’re looking for a steakhouse ambience, Butcher & Singer and Barclay Prime are Starr’s steakhouses and they’re a little nicer than the main chains, which also exist in Philly. Urban Farmer near Logan Square is also supposed to be nice. If you do prefer a chain, there is both a Del Frisco’s and Del Frisco’s Grille - I haven’t been to the former, but the latter is pretty nice and a good place for a business casual dinner. That one is closer to Broad Street, which might be convenient if you’re staying near there.

The Dandelion (upscale pub theme) is pretty good, as is Gran Caffe L’Aquila. Gran Caffe is an Italian place and their upstairs area is nice for a group dinner. If you tell us where you’re staying and what kind of food you want, I can provide slightly more targeted recommendations.

Fork Restaurant is good

Parc - French restaurant right on Rittenhouse Square.

Looking to make a dinner reservation for 6 work colleagues. Any recommendations from dcurbamoms?
No real dietary restrictions, but nothing too adventurous