Phone mutes itself during calls, randomly places calls

My iphone 6 will mute itself during phone calls when nothing is near the phone. The contact list also pops up and it will make an outbound call to a random contact while I'm on the phone. Nothing is touching the phone when this happens. The phone can be on the table and it will happen. It has been happening a long time and I've live with it. It just muted several times during a 5 minute call. This is such a common thing that family and friends know to tell me I've been muted rather than assuming I've had a call failure. It can occur when I'm on speaker, bluetooth, wired earbuds, or holding the phone to my ear. It has carried across a few IOS versions. I didn't find a question answered on here, but found many online questions about it in other forums. No one had an answer from Apple so thought I'd ask for a solution here. All other features on the phone work great, but since it is a phone...well, it would be nice to make calls with it and not have it randomly mute or put my calls on hold to call someone else. For what it is worth, the numbers it calls have nothing to do with my recent call list. I'd appreciate any assistance.