Percocet is a Schedule II controlled substance and prescriptions for Schedule II medications cannot legally be filled or refilled by telephone. Federal law requires a new prescription for Percocet each time you get more of it.
So if you need more Percocet, you need to make an appointment with your physician. He might prefer to be able to call in a refill, but that's just not permitted, not anywhere in the United States.
I'm a physician and medical director of a hospice. I am thoroughly familiar with the federal narcotics regulations as well as those of the state in which I practice.