Erased find my iphone for an insurance claim and my phone has reset

I have damaged my iphone and therefore raised a claim with my insurance, in order to do this i need to remove find my iphone... no problem, iphone erased from find my iphone. I then look at my phone 2 minutes later to see the apple logo and a loading bar, the iphone then comes back on and it's like setting up a brand new iphone.

I haven't completed the steps as i don't know which step is best to take as i haven't backed up my phone as i was planning on doing that this evening as the claim takes 24 hours to be responded to, i can't remember when i last backed it up and i'm not an icloud back up fan.

How has this happened and how can i fix it?