Have a panoramic router with phone line issues

I have a Panoramic router with a Panasonic wireless phone system connected to it. Sometimes, when the phone rings and I answer, I can't hear anyone and they can't hear me. It does it just a couple of times a day but can be frustrating to both parties. I upgrated the router, no help. Switched to different phone manufacturer, no help. Unplugged the printer which is on wifi to see if the printer was trying to use fax line, no help. I've run out of ideas.