The greater Phoenix area is one that is covered by Bing photogrammetry, so it is among the highest-resolution and most detailed areas in the sim (which includes Phoenix and all of the communities around it, like Peoria, Anthem, Carefree, Tempe, Mesa, Chandler and San Tan Valley).
As is well known, the simulator uses Bing Maps for the photo scenery, so if anyone wants to check what the quality of their area may be in the sim, you can preview it by checking out the area in Bing Maps. Outside of photogrammetry coverage, Azure AI determines from the photo scenery what buildings (including shape/height/colors) and plant life should be depicted in the sim. Among the monthly updates that will be provided by Microsoft following release, there will be updates to the photo scenery whenever there are updates put into Bing Maps.