It's important to THIS doctor, that he be called that, and he is your customer.
Many docs, both MD and PHD only desire the honorific be used in front of patients, students, residents or if they are introduced by another in a professional situation. In a social situation if intro'd with the title, they will say "please call me John" to make everyone feel more at ease. One of the least pretentious men I ever met had multiple doctorates, a peerage, and was a full tenured professor at Oxford. Anyone that knew him, knew to intro him as just "John Smith" in a social setting. He was gracious, welcoming and unassuming, a real classy guy. I never once heard him intro himself as Dr.