I use two different methods.
1. This is good around dinner time. I explain that I don't have time to speak, but if the caller can give me their home number, then I will ring them later at home when I have time, no doubt when they are about to eat their dinner. When they object I just keep asking for their home number. They soon hang up.
2. Much simpler. I say that I am busy, and can they hang on for a minute. I then put the phone on the table and carry on with my life.