I have been experiencing the same issue with echo for about 2months. Doesn't have anything to do with Bluetooth in my case. The person I'm talking to will tell me they can hear themselves echo....neither of us will be using Bluetooth.
It's very frustrating and intermittent. I find myself putting off important calls until I can do so from a landline so my caller doesn't have to deal with this embarrasing problem. I called Verizon and they told me they couldn't do anything and I'd have to bring the phone into the store. In their usual fashion, they act like I'm the only one who ever reported such an issue.