Iphone 6 echo

All of sudden I have an echo during phone calls. I can hear myself echoing. Any ideas?

 

I reset network settings, restarted the phone and it seems to be resolved for now. Thanks for the reply. I've had echoes with Lifeproof cases when I used speakerphone on my end but never had this issue without. One call was to my husbands flip phone, one to a landline. The receiver couldn't hear it. Only I could.