Storage

In such a situation, you won't be able to create a backup to iCloud any longer NOR sync any data from iPhone to iCloud.

And be careful: sooner or later, many functions of your iPhone may also be affected.

The only solution is to buy a 50 or (better) 200GB iCloud extra storage plan, following these instructions:--> Upgrade to iCloud+ - Apple Support, as per these price lists:--> iCloud+ plans and pricing - Apple Support

Forewarned is forearmed.

Regards

Giulio

That warning message might be referring to iCloud Storage. See this article:--> What's the difference between device storage and iCloud storage?

Regards

Giulio

Please check: Settings>[your name]>iCloud>Manage Storage, and post back a screenshot.

Thanks and regards

Giulio

You are welcome