If you are exempt, you must be salaried. Under the law, an exempt employee MUST be paid if they do any work in a day--if you work at all, you get a day's pay. Only if you don't work at all would you not be paid without the use of PTO. This does not mean that you can miss work with impunity, of course--you can be demoted, suspended, terminated, etc. for missing more work than they think is appropriate. But they can't make you, as a salaried employee, use PTO for a partial day's pay.