Thanks for visiting the Apple Support Communities. I understand you are trying to backup your iPhone. I am happy to help with this.
This article will help you make a backup in iTunes or iCloud: How to back up your iPhone, iPad, and iPod touch - Apple Support
If you have trouble backing up your iPhone, please check these articles out. The first is for trouble making your backup with iCloud, the second for iTunes.
1. If iCloud Backup couldn't be completed or you can't restore - Apple Support
2. If your iTunes backup couldn‘t be completed or you can‘t restore from a backup
If you still have issues, please provide us with any info about this, including any alerts or error messages you receive. Thanks and have a wonderful day.