Backup to iCloud
I backed up iPhone 6s iOS 11.1.2 to iCloud but nothing was transferred to iCloud. Why?
iPhone 6s, iOS 11.1
How are you verifying this? If you go to Settings on your iPhone where you turn the iCloud Backup feature on, that will tell you the last time you backed up to iCloud. You can also go to iCloud.com on a computer and see your iCloud usage to verify that there is a backup taking space, but no details.
Or, perhaps you're not understanding what a backup is. An iCloud backup is not all the individual files, apps, etc. that you can access on your iPhone. A backup is an encrypted file that clusters all these things together which you cannot open.