It's dangerous to think about yourself in that way. Everyone is good at different things and you don't have to be perfect at everything. From my experience dealing with anxious people is that it's often much more exhausting to deal with the excuses and self-blaming than any actual trouble they (think) are causing. If your colleagues are fine with picking up the phone for you then don't even mention it, you can do something else for them later if you feel that you have to compensate.