Getting files off a dead iphone 6

My iphone 6 got wet and will not turn on. I understand I need a new phone and I am ok with that.

The big problem is the gentleman at the apple store said my icloud backups were incomplete and therefore useless. The syncs I have done with my computer did not create a backup either. If this phone was a laptop or desktop, I would just pull the hard drive, connect a cable to it and copy it to another drive. What options do I have with my iphone?