I had this same problem after 8 months.
Took it to the Apple Store, they replaced no questions asked. My new one started doing it 5 days after getting t home. I'm also starting to think the problem is related to putting the phone in my rear pocket. But it's the only pocket that holds the phone. This is a weak ass vulnerability. How could this pass QC? Luckily I only have 10 minutes to go to get a new hand set. I'll update if I get another replacement.