I have been denied PTO multiple times. My boss recently told me that he will deny PTO based on the reasons employees give for using PTO. He asks about PTO and vacation time and what you are using it for. Last year I lost 2 days of vacation time due to denials like this. Our company has no policy on paying out vacation or PTO if you are going to lose it. Is it legal for my boss to deny based on why I want to take time off?

It is. Is there a company policy to which your boss is adhering?

OTOH, if he wants to play this game, why not just give the answer he wants to hear? You should know by know what kinds of "reasons" get approved and what kind don't.

There is no company policy that my boss is following he is just being a dick. I don't see how this is legal or legit.

It is legal because there is no law that says it is illegal.

Seriously. There is no Federal law, and no law in Arizona (or any other state for that matter) that requires that you even be GIVEN paid vacation or PTO, let alone that prohibits your employer from denying a request.