Thank you very much"I'm sorry for having missed your call. "
To me there is a suggestion of distance between the speaker's acts and the 'missing.' If I was in California on a trip when the call came to my New York office, I might later say that. I would not go so far as to say that I made to trip to avoid the call, BUT the phrasing suggests further a lack of regret, or maybe "It couldn't be helped." Hence the 'sorry' is perhaps, pro forma, a routine phrase that's part of "Let's get on with other things."