My guess is that neither the person on the other end of the phone, nor the schedule nor your staff member got the quality of attention they really needed. Imagine a two year-old is looking for attention and you are busy. To take care of a two year-old you have to drop what you are doing, get down eyeball to eyeball and give them your undivided attention for about five seconds. If you do this, you'll buy yourself some time. The only difference between dealing with children and adults is that kids are more honest - they will not pretend that they have your attention if your mind is wandering.
Adults are usually more polite but no less observant.
The truth is that you can really only concentrate on one thing at a time anyway. If your mind is occupied with extraneous thoughts your attention is not fully with the person in front of you. Even if they do not call you on it, they will notice and keep coming back again and again trying to get through to you. As with children, you can handle an situation in five seconds or five hours - the only difference is your level of presence when you do it. So the secret to productivity is to handle things exactly the way you would with a child.