There are grey areas with a bit of wiggle room. That much is certain. I've worked with practices/doctors where you're always routed to a call center. I've also worked with practices/doctors that actually pick up the phone from time to time.
But business is business and people are people. Things can get difficult and messy quick. A lot of doctors are people, engaged in business, as well as medicine. Sometimes business relationships end on bad terms.
Sometimes another local SEO is actively throwing wrenches in your program. It's all local business, so it's always a small world. Say they somehow know Dr. Smith has left the practice.
"Hello, I would like to schedule an appointment with Dr. Smith."
"Dr. Smith has left the practice, may I schedule an appointment with Dr. Jones?"
"No thank you, have a nice day."
Goes on to edit all Dr. Smith listings as closed.
And that's just one potential outcome.

I'm not a dyed-in-the-wool sales person. It keeps conversations natural, as well as likely.