Can't backup broken iPhone 6 without entering pin

I have recently broken the screen on my iPhone 6 and want to back everything up before I take it into apple to be repaired.

My problem is when I go to back the phone up in iTunes, it wants my pincode. I can't put my pincode in as my screen is broken!

The screen seems to be responding to key presses as it vibrates when I touch the screen where I think the numbers are, but this still doesn't work.

Does anyone know a way I can get a backup of my phone despite this issue?