How do I get more storage on my device

Perhaps these links will help you manage storage. As you delete, be sur to save important data and photos to your computer of external drive.

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

Clear Other storage on your iPhone or iPad - Apple Support

You delete things you don't need, want or use. There is NO way to add memory to iPhone. It's physical memory was fixed at purchase.