Boot loop - cannot update/restore

(Doing this on the behalf of someone who is currently unable to access their Apple ID and is currently overseas)

iOS Version: 11.4.1 Build 15G77

Device: iPhone 6

Not jailbroken and never has been

Uses iCloud to backup - last was 26th of Aug

Last online: 3rd of September (According to MDM)

Had the battery replaced on the 6th of July by one of the Apple Stores

Prior to the battery change, all iOS apps were crashing. Getting a new battery fixed this. (Device was restored too)

I will keep this as simple as possible but also try to explain it sufficiently.

So the phone has no storage left and now it only shows the apple symbol when booting up, nothing else. I believe that it is stuck in a boot loop. I have seen other users have the same problem with no solution to the problem.

On a friends computer, the person attempted to update the device via the latest version of iTunes however the update failed and stated that it must be restored.

Cannot restore due to the two-factor authentication code which is sent to that device.

The image below shows what happens before updating/restoring:

Since the device is recognised, I have considered suggesting the use of a 3rd party program such as "dr.fone" in order to attempt to recover data/ remove the loop. Wanting to keep restoring to the last resort.

Would appreciate any suggestions.