iPhone storage

you don't apart from purchasing a new phone

icloud storage is not something which adds to the phones local storage

read

Manage your iCloud storage - Apple Support

Instead of buying new storage, you could always put all of your photos on google photos and delete the app so the gb and storage goes away without not having any of your photos.

All of your pictures will be saved if you keep them on google photos even if you delete the app. :)