What capacity of heat pump is needed for a residence near Phoenix, Arizona?
The Number of Windows and sliding glass doors also play into the calculation, it sounds like you have good insulation, but that area gets much hotter than where I live. Some of the calculators on line are focused on energy savings and provide questionable advice in my opinion. The best way to find out would be to talk to neighbors with similar sized homes. Ask about Thier unit size, power consumption and if the units cool well when the temp gets into the 100's . If they want to size the unit on square footage alone (unless the company can show a very similar home) find another company because Windows and doors add a large cooling load even if double Payne. Many years ago before I got my HVAC license I had a 2900 sf home with 26 Windows and 3 sliding glass doors. The company recommended a 3.5 ton unit, I thought that would be two small after talking to a neighbor with a similar home that had a 4 ton and said it was not enough. I had a 5 ton installed and on the hottest days that was not enough to keep the home at 78F.