Why is my phone saying
Ready for your new iPhone
Your data is ready to be moved to your new iPhone. This iCloud backup will be deleted in 21 days.
The following Apple article describes temporary iCloud storage. Get temporary iCloud storage when you buy a new iPhone or iPad - Apple Support
I don't know of a reason that you would get that message if you didn't create a temporary backup but I have seen a few other posts in the last month or so wondering about the same thing.