iCloud can be removed from an iPhone with iOS 8 by going to Settings and selecting iCloud, then selecting Storage, tapping the Manage Storage option, and then tapping the name of the device you'd like to remove from iCloud. From there, tap Delete Backup.
If you have iOS 7 on your device, instead of choosing Storage, choose Storage and Backup. You may also remove your iPhone from iCloud from your Mac computer. Open the Apple menu, and select System Preferences. Click on iCloud, and then click on Manage. From there you select Backups, which is located on the left side of the screen. Then select the iPhone you want to disable from iCloud, and click Delete. If you don't see Backups on the left, your iPhone is not currently connected to iCloud.
You can also remove iCloud from your iPhone on a Windows computer. You need to open iCloud for Windows, and then choose the Storage option. Click on Backups on the left of the screen, and select the iPhone you'd like to remove from iCloud, and then choose Delete. Again, if you don't see Backups on the left, the iPhone is not currently connected to iCloud. Removing iCloud from your iPhone prevents your data from being preserved in the event your phone is lost or damaged.