I got my wife a iPhone 14. I can’t backup her old one to transfer the data

iPhone to iPhone, there are three ways,

1. Quick Transfer using Bluetooth (Does not require Internet) --> Use QuickStart to transfer data to a new iPhone, iPad or iPod ...
2. Restore from iCloud Backup (Does not require Internet) -> Restore or set up your device from an iCloud backup - Apple ...
3. Restore from iTunes backup (Does not require Internet) --> Restore your iPhone, iPad, or iPod touch in iTunes on PC ...

What was the result when you followed the guidance in the Related Article above your name on this page, that you were reading just before you posted here? If the Related Article doesn't answer your question please post back with more details about the issue and another user in this user-to-user forum will try to help.

While it’s always a good idea to back up regularly, or ideally automatic nightly backup, you don’t have to back up just to transfer content to a new phone→Transfer data from your previous iOS or iPadOS device to your new iPhone or iPad - Apple Support