iPhone Software Update 12.1.2

My iPhone 6 updated to iOS 12.1.2 over the air. Now that I have connected it to my Windows PC, iTunes version 12.9.2.6 tells me I have iOS 12.1.2 and need to update to 12.1.2 :-) When I click "Update" the software downloads, extracts, and then either my phone goes into a continuous "backup" mode, which I have to crash out of by switching it off and terminating iTunes, or i get an error message saying my phone could not be updated and it disconnects from iTunes. Any ideas?