I've had my 6 plus since Christmas and the touchscreen keeps locking up/freezing. I have to power off at least 5-8 times everyday and I have missed calls because the screen won't respond. Has anyone else had this problem? If so, how did you fix it?
This isn't a common thing. I would take the phone to an Apple Store since it still less than 1 year old. That is your best bet for quick fix and likely replacement.
If you go to the Apple Store don't forget to set an appt via the Apple Store app. They may refer you to do a backup first, and a restore to see if that helps. I'd suggest doing a full backup and prior to doing a restore see if you can set the phone up as new and determine if the issue is still happening. You can always restore the device at anytime after you try this.