So you are running out of space on your iPhone , why not start syncing your photos and storing them on Google Photos.
When you save them on iCloud , your photos are synced across all your devices.
If you take a photo on your iPhone , it adds on all your devices , computer , tablet – through syncing over iCloud. If you delete a photo on your iPhone it deletes across all your devices , but sometimes you run out of room.
Google Photos allows you to delete the photos from your device ( iPhone , Android ) after it has been uploaded to Google photos.
Lets also remember Google Photos is free.
Instructions on how to do this can be found here: