How to Turn Off Automatic iCloud Backups on an iPhone

Open your iPhone's Settings. Do so by tapping the grey gear icon on one of your Home screens (it might also be in a folder named "Utilities").

Scroll to the fourth group of options and select iCloud.

Scroll to the bottom of the page.

Select Backup. This is above the "Find My iPhone" option toward the bottom of the screen.

Slide the iCloud Backup switch left to the "Off" position. It will turn grey, signifying that your phone will no longer automatically back up to iCloud.