What will you do if your customer keeps getting phone calls during a meeting?

You are helpless.It is the basic decency that is to be followed by both if in a meeting not to divert the attention to a phone call. The maximum what u can do is to inform the caller that u r in a meeting and u will get back to him later. 

Offer to take a break in the meeting so they can address the incoming calls.

As a salesperson, there is nothing you could do.

But most of the times, customers will only take calls that are important and other times, they will put their phones on silent.

The answer depends on the duration of the phone calls and the kind of customer.

If small durations which is few seconds why not. While if ten minutes. You can inform the client that you have other meetings and will determine another appointment.