I upgraded to 2 TB of storage but keep getting notifications s that my storage is full

You’ve got 2TB of iCloud storage, but that makes no difference your phone storage, which cannot be increased.

The related article you’ve apparently come from explains.

Hello ~ Carefully work back through this article as your device storage is full not your iCloud storage…

What's the difference between device storage and iCloud storage?

~Katana-San~