Have you tried booting the phone into Safe Mode to see if the issue still occurs when all the third party applications are disabled. If it doesn't reoccur, then an application you downloaded is causing the rebooting. You will need to remove that application. If it does reboot while in Safe Mode then you have a deeper problem.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
TDTECH, we don't want this to be an ongoing problem. When did this issue start happening? Did you recently update the software on your phone or download a new application to it? Does your phone have any physical or liquid damage?
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After factory resets and removing the SD card didn't work, VZW tech support tried to get me to reset again, but not sync my accounts to the phone. They think there is garbage synced to google causing the reboots. After realizing my other 3 android devices don't have this issue with the same accounts, I decided against this. I'm eating the $250 I have left on this phone, and I ordered a Pixel directly from Google.