Receiving or calling my phone volume goes to near zero after a series of beeps like someone dialing.

My brother in Phoenix calls me and in middle of call we both hear beep beep beep like a dialing sound. Then we can barely hear each other for a minute or two. The volume comes back until the entire process begins. He’s 90 and no longer can deal with this type of situation. I have same COX system with phone and want to know what to tell him. Should he just switch to whoever is local phone company? I suggested he call COX,  but he does not call.