Final answer:
A physician can't request refills on Phenobarbital over the phone because it's a Schedule IV controlled substance requiring a written prescription for refills.
Step-by-step explanation:
The physician cannot request refills on Phenobarbital over the phone. Phenobarbital is classified as a Schedule IV controlled substance according to the Controlled Substances Act, which sets special restrictions on how such medications can be dispensed. In most cases, to prevent abuse and ensure proper monitoring of use, regulations require a written prescription from a physician for refills, rather than a phone-in request.