Can I buy more storage

Note there's different kinds of "storage". Click on this link to learn the difference between your device and iCloud storage, ways to manage your space, and upgrading to iCloud+ if you need more --> What's the difference between device storage and iCloud storage? - Apple Support

Read this support article to learn how to how to check the storage on your iPhone and iPad, and how to utilize iCloud to optimize the storage on a device --> How to check the storage on your iPhone and iPad - Apple Support