Phoenix is the fifth largest city in the US. Going to be a heck of a natural experiment as it only keeps getting hotter, and how long it takes for the climate migrations to occur.
But if we take metro areas (MSA) -- which is somewhat more representative of size -- it falls off to 10th place.
https://en.wikipedia.org/wiki/Metropolitan_statistical_area#...
It's still quite high. I'm surprised so many people like to live in hot places. I'm told it's a "dry heat" though, so it's not as bad. You can use swamp coolers to cool down.
Hot and humid places are more uncomfortable. Houston in August is 110 F with 80+ % humidity. It's oppressively hot.
Drier than the south still isn't dry enough when it's 117°F with a dewpoint of 65°F. You'll end up with output temps in the high 80s (or higher), and the output air will be extremely wet.
These things have to be a choice for people
A lot of people choose sun
The key to enjoying Phoenix is understanding that from October to May or so, it's basically San Diego. That's when you do all your outside stuff, you walk places, you have a great time. Then from May to October it's the surface of the sun.