I'm not in Phoenix very often despite living not super far away in Tucson. But I was in the area for work, and was trying to figure out a quick lunch spot to grab something to eat in between. I found Lux, which is a solid place. Was lucky to grab a spot in their smaller parking lot and ordered the grilled cheese w/tomato soup for lunch, which was quite tasty. The staff was also really accommodating and friendly, which goes a long way in my book.
Lots of other folks were there, many of whom were also studying/working, but there still seemed to be a number of places to sit. I didn't have much of a hankering for caffeine when I was there, so I didn't get the chance to try one of their many coffee offerings, but I'm sure they are also delicious. Would recommend for a quick and tasty bite if you're in the area!