iPhone storage

No you cannot purchase storage for your phone. It will always have the same amount it came with. The only way to gain more storage space is to delete photos, messages, apps, etc.. Be sure to save important photos and data to your computer or an external drive. Check these links..

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

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

You can't increase your phones storage space.

iCloud storage is online backup.