"You are standing" is simple present. "Standing" here acts somewhat like an adjective, instead of a verb.

तुम खड़े हो should also be correct, more respectful than तू as well.

तू है, तुम हो, आप हो, आप हैं, the 4 ways to say you are, more formal with each one. हौृ हौ and हाु are not words