Unresponsive iPhone 6s

Issue: Unresponsive iPhone 6s v11.1, looping between Apple icon screen, unresponsive keypad, self restarting

I was on a phone call when my phone failed. I got a black screen followed by the Apple icon. After much waiting, and multiple hard resets, the key pad eventually appeared but was unresponsive. The phone now keeps going through a loop - icon screen, unresponsive keypad, reboot, icon screen etc etc. Also, I noticed that the lock screen wallpaper is an old one I used previously.

I have since plugged it into iTunes to reboot it but it asks me to enter the passcode despite the keypad not being visible or responsive. The only solution around (as per Apple) is to go into recovery mode. Initiating this, the phone asks me (through iTunes) whether I'd like to upgrade to v11.1.1 or to erase the phone and bypass the passcode.

I am stuck at this stage, trying to find a solution without the need to erase the phone. Any advice would be great.

*The phone is in excellent condition with no previous issues and encased in a military-grade protective case.