Quote Originally Posted by Layne
So what do you call a doctor? Not neccessarily a medical doctor but, say a PHD in physics.
In a direct conversation stick to use full first name and patronymic. Even when you're talking to a president that will be a polite form of address. When referring to some professor who is not present or in writing you may say Профессор Иванов (Surname only).
Don't use Доктор at all when addressing people. There's no need and otherwise your speech will be pompous and formal.