So I bought iPhone storage but it’s still full

After you have read the link in blue above your name on this page, you will realize that you have bought space in Apple's synching service iCloud. You cannot buy more storage space as the phone will always have the amount of storage space it came with. the only way to gain space is to delete photos, messages, apps, etc.. Be sure to save important photos and data to your comuter or an external drive. this video may help...

iCloud storage can only help in a limited way with a shortage of storage on an iPhone. See the information in What's the difference between device storage and iCloud storage? - Apple Support including the following:

Free up space on your device

Using the steps above, you might see a list of recommendations for optimizing your device storage, followed by a list of installed apps and the amount of storage each one uses. Tap an app's name for more information about its storage. If you don't see any recommendations, try these steps:

• If you use iCloud Photos and turn on Optimize Storage, you can lower the amount of storage that your photos use on your device. 
• You can remove content from your apps like photos, music, and podcasts. 
• You can delete apps that you're no longer using.

Learn more about how to optimize the storage on your iOS or iPadOS device.

Carefully read and understand the article linked above.

As it explains, you bought iCloud storage. You need to empty some iPhone storage.

Also:

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