Not enough storage space to perform successful backup.
Not enough space to perform backup. What type of items use the most space? Is it pictures and videos that need to be deleted in order to free up space?
iPhone 8 Plus, iOS 13
Question marked as
Yes, it usually is media like pictures and videos.
To know more about iPhone Storage and how to manage it: How to check the storage on your iPhone, iPad, and iPod touch - Apple Support
and specific to your query: Manage your photo and video storage - Apple Support