If you ran out of iCloud storage while you had your iPhone 12 Pro, and didn't fix that, then
- Your iPhone 12 Pro would have stopped making backups to iCloud
- If you were synchronizing data to iCloud, your iPhone 12 Pro would have stopped uploading new data to iCloud. (E.g., if you were using iCloud Photos, it would have stopped uploading new photos and videos.)
You can upgrade your iCloud plan – and that would be a good thing to do if your iPhone 14 Pro needs more space for backing up and synchronizing data.
However, even if you upgrade your iCloud plan, it seems unlikely that your lost iPhone 12 Pro is going to be in any position to upload more data to iCloud. There are many, many things that would have to go "right" for there to be much chance of further uploads, and realistically speaking, the chances of all going "right" are slim and none.
What do you see when you log into https://www.icloud.com/ ? If you were using iCloud Photos, any photos that actually made it into iCloud would be there.