Remember when you were a student and went into your professor's office hour? He always seemed to be very busy, hardly had time to set down, and your conversation was always interrupted by the phone ringing? You probably felt uneasy and thought your minor problems would disturbe some very important things going on, if your professor even had to answer calls during dedicated time slots for students.
I have a phone in my office. Nobody ever calls me.
I hold office hours once a week, it's a two-hour slot. Two weeks ago, no student came. No phone call.
Last week a student came to discuss an idea for his PhD project. He was in my office for maybe 10 minutes and the phone rang twice. One call was from a technician asking if this office was indeed my office. The second call was from the secretary, asking if I was still in my office. So, nothing really important, but the student started to feel uneasy. When he left, no other student was waiting and nobody else called me that day or the day after.
So getting phone calls during meetings seems to automatically come with being a professor. Maybe the calls my professors got when I attend their office hours were similarly important. And there may be more things coming automatically with being a professor contributing to the "professorial aura."
For students: please don't think you would disturb your professor when you make use of dedicated office hours, he or she reserved that time for you.