I just bought more storage. Why isn’t it showing on my phone?

You bought iCloud storage, NOT iPhone storage. Your phone comes with a fixed amount of storage that is not upgradeable. You chose how much storage you wanted when you bought the phone. What you can do is offload some of your files/data from your iPhone to iCloud to free up some room on your device. Things like music, photos and such can be synced to iCloud and become available online.

iCloud storage is independent of iPhone storage. If you need more space on your phone, you will need to delete something.

You can’t increase iPhone storage.

iCloud storage is online backup.

If you need space on your iPhone, you have to delete stuff.