How to add more device storage

You cannot add more storage to your phone. It will always have the amount it came with. Check the link in blue above your name on this page to see the difference between device storage and iCloud storage. the only way you can get more space on the phone is to delete, photos, messages, apps etc.. Be sure to save imortant photos and data to your computer or an external drive. This video may help...

You can't.

You will have to delete stuff to free up storage space.