I just purchased more storage but my phone says my storage is full

You cannot purchase more storage for your phone. It will always have the amount of storage it came with. You purchased space in iCloud, Apple's synching service. See this link ...

What's the difference between device storage and iCloud storage? - Apple Support

To create more space, you must delete photos, messages, apps, etc.. See these links...

How to check the storage on your iPhone, iPad, and iPod touch - Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

iCloud storage is not the same as storage on your iPhone.

You can’t buy more storage on your iPhone itself but here are two links that can help you to free up storage on your iPhone:

https://support.apple.com/en-us/HT201656

Optimizing photo storage on your iPhone can help a lot

https://support.apple.com/en-us/HT205703

Your iPhone's memory and iCloud storage (what you buy) is not the same.