My iPhone storage is full, how do I correct that?

The only way you can create more storage space on your phone is to delete photos, messages, apps, etc.. Be sure to save important photos and data to your computer or an external drive. Check this link...

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

Video may be helpful...

https://www.youtube.com/watch?v=bnhuHSv_WrI

Perhaps this article will help;

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

You cannot add any more storage to the device. That was fixed when you bought it. You can only optimize the storage you have.