To make sure that this is not software related, set it back to factory settings, without using any backup data afterwards. Set up the rest of the personal settings manually and test the phone.
Use iTunes to restore your iOS device to factory settings - Apple Support
If the phone works as before the update, restore from the latest backup. If the problem comes back, the backup data contained corrupt data, causing your issues.
You might have to reset the phone and connect it in recovery mode to restore the phone, described in this article:
If you can't update or restore your iOS device
If it still does not work, this is a hardware issue and the phone has to be serviced by Apple or an Authorized Apple Service Provider:
Find an Apple Authorized Service Provider
iPhone - Contact Support - Apple Support