This is what we did (for iphone 13):
1. On some other apple device, (BUT FOR YOUR PHONE’S APPLE id) ensured we had sufficient iCloud storage available – if not, increase the iCloud storage via your alternative apple device
2. On our laptop (Windows 10 ), ensured that we had downloaded the latest version of iTunes. (This did not work on my Mac so I used a windows 10 based laptop).
3. Do not turn off the phone.
4. With our security locked phone disconnected from our laptop, placed it into recovery mode. If you forgot your iPhone passcode - Apple Support http: //support.apple.com/en-mide/HT204306
5. Press and hold the side button for your phone whilst connecting it to your PC. Don’t let go of the button.
6. Keep holding the button until you see the recovery mode screen on your iPhone, then let go
7. If you see the passcode screen, you needto turn off your iPhone and start again.
8. Located iPhone in iTunes on the computer that it’s connected to and pressed UPDATE (NOT RECOVERY – that would have the effect of erasing everything on your phone)
9. Download the latest iphone software update on iTunes
10. Repeated steps 4,5,6,8
11. Made sure our iphone stays connected to our laptop the whole time and wait for the software update to sync with our iphone
12. Once the software update was complete, waited for 8 hours and then input our passcode
13. Phone was connected to home wifi (rather than 4G) so connected phone to Mac and let it syc to iCloud – depending on the number of photos on your phone, it may take up to 24 hours to uploadphotos to iCloud (hence the importance of step 1). You will see the photos being uploaded to iCloud on your Mac.
14. When the data upload to iCloud is complete, we were able to restart our phone as normal and it did not require a factory re-set !! All of our contacts were on the phone, and all of the photos were in iCloud!
I am not sure why Apple support could not advise us on these steps as it would have saved a huge amount of heart ache and upset.