backing up iPhone with data only. No wifi

I did see that, but you don’t need WiFi to back the phone up to a computer. I’m merely assuming that you have a computer as most people do these days. I personally back my phone up to both the cloud and my computer. I then back-up the computer to an external drive. The back-up to an external drive does not use WiFi either. Backing up to a computer requires only the proper cable to attach the phone to the computer depending on model, etc.

Check this link...

How to back up your iPhone, iPad, and iPod touch - Apple Support

You cannot create a backup on iCloud without a connection to a WiFi Network.

Axel F.