Many ppl seem to like the cellphone idea and its cute. But what will you do if someone actually calls you while you’re supposedly already on a call and your phone rings? You cant do this every time you go shopping! Also this is not solving the issue but avoiding it.
I think acting politely but cool or involving your family is a much more sensible approach.
But tell us, is he a family friend/someone you have contact with outside of the store or not? Any what type of messages or vibes have you given him in the past?