How do I free up storage on my iOS device?

Here are some helpful articles that can guide you on how to free up storage space on your phone.

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

Manage your photo and video storage - Apple Support

Clear Other storage on your iPhone or iPad - Apple Support

move all the data to mail accounts or purchase the iCloud for more storage and back up all the data to iCloud.

then delete the data in the device .