i want to backup my iphone music on icloud

What does iCloud back up? - Apple Support

Short answer, no, iCloud cannot backup your Music content. Thats up to you as the user to ensure its backed up someplace. It's not a default option in the system, but yes in theory you could put all your music in iCloud Drive and access it through the Files app, but then you lose a lot of additional functions that the Music app provides to you.

iTunes purchased content can be downloaded to your PC and backed up for safe keeping, but content that was synced to your iOS device from a computer can not be removed from the iOS device. There are copyright protections in place that only allow syncing of Music content on a one way track. There are third party softwares that claim to be able to copy that data off the device, but you take your data security into your own hands at that point as third party software not sanctioned by Apple may carry the chance of damaging the software of your phone.

If the data is on a computer currently, invest in an external hard drive for backup purposes of that machine. Or, use a cloud backup service for the computer that covers all files. Like carbonite. If the files you are questioning are on the phone already, I can make no suggestions that could compromise copyright laws in pulling data off that device. You will have to research that on your own.