I know this is an older thread, but in case you’re still having trouble:
I dealt with this for a year!!!! Super annoying and couldn’t wait until it was time for a new phone. My daughter had the same issue. She took her screen protector off (one of the harder ones, not just a film that goes over), problem solved! So, I tried it, thinking there was no way that was it...problem solved! My phone hasn’t done this in 4 days! I was having trouble all day everyday. The phone would even call other people while I was on a call. I hated it! Anyway, apparently the screen protector was causing issues with the screen sensitivity. Hope this helps!