Help me on backing up my old device please

If you don't want to wait for your iPhone to back up to iCloud, the other option is to back it up to a Mac.

Ref: How to back up your iPhone, iPad, and iPod touch with your Mac - Apple Support

If what I provided you won't work for you, you can contact Apple Support directly for assistance with this issue. To do so, select the "Support" link on the lower-left hand side of this forum's web page.