The cost of buying is now significantly higher than the cost of renting in Phoenix. I believe this may be causing the build up in inventory in Phoenix as when people are presented between buying and renting they see that renting is significantly cheaper.
The median sale price is also up 20% YoY and closer to 100% over the last few years. While this is not as important as the monthly payment is still means you need a much higher down payment.
Median monthly payment went from 1600 a year ago to 2560 today (at 10% down)