Sadly you’re the 2nd person I’ve read about that’s reported they can’t use the new iD Mobile app on their iPhone due to your phone not being able to be updated to a high enough iOS.
So, the only thing I can suggest is to use the online method instead. This might not be the ideal solution but at least you can get to where you want to be:
https://my.idmobile.co.uk/login
This above link would also work on a laptop/PC/tablet etc without the need for the app.
HTH
Hi @Paul Mangan
Unfortunately your device may be too outdated for usage with the iD Mobile app, it may be worth trying the website as suggested above by @Daz_S.
Tom