Did you know you don't have to answer the phone when it rings? If I am in the middle of something I don't have to drop everything and run to answer the phone. Some people have a pavlovian response to the ringing of the telephone and feel compelled to answer immediately.
In an age of voice mail and answering machines you can actually call somebody back. If it is important they will leave a message. Remember the phone works for you, you don't work for the phone.
What would happen if you let your phone ring?