How do I get more storage on my iPhone?

If you need more local storage than your current phone has, then you need a new phone.

If you have a lot of photos and videos, and have enough iCloud space, and are using iCloud Photos, you can turn on “Optimize iPhone Storage” on your phone. This gives it permission to substitute lower-quality, space-saving local copies of photos for full-size ones. But the system makes the decision as to when to use space-saving copies.

You cannot add any storage to a phone. If you need more storage, you will need to delete whatever you don’t use very often. The only other option is to buy a new phone with more storage.

Then you need to purchase a phone with more storage on it.