That’s pretty reasonable for the Phoenix market - large area with lots of pools. If you haven’t gotten other quotes, then you really won’t know for sure. Given the market base in your area, you should be able to find at least 3 or 4 reputable plaster applicators to get quotes from. Down south here we have fewer contractors to pick from but we do have a few well-established family businesses to choose from.
As I always say, you should ask for references or pools that have been recently worked on. A good contractor is always eager to show off his workmanship.