I have three go-to spots for dim sum in Phoenix - Great Wall, Phoenix Palace, and C-Fu Gourmet. They all have their pros and cons, but C-Fu has won me over with their service. They're the only one of the three who have staff who are courteous and make the effort to speak to you in English. However, food-wise they're more or less on par. The dishes at C-Fu sometimes look re-heated, but that might be because I'm not a morning person and don't make it in til 1PM or so. But it's still pretty damn good. Great Wall has really good barbecue pork buns, but are always jam-packed on any given day, so be prepared to wait outside for about 15 minutes for your number to be called - keeping in mind that 15 minutes in the summer heat feels like an eternity. Phoenix Palace has pretty good egg tarts, but can get pretty crowded too and have some rather rude waiters.
So if you wanna try dim sum, I'd recommend trying out all three to try their best dishes. If you don't want to have the experience ruin your day, go to C-Fu.