Navigate to Settings > iCloud > Find My iPhone and toggle it off.
Navigate to Settings and click on your name. Scroll to the bottom, and tap "Sign Out".
Navigate to Settings > General > Reset and tap "Erase All Content and Settings".
Sometimes, when you are busy or out and about and your iPhone starts ringing, you don't want to pick it up, but you know it might be so-and-so with that important call you've been waiting on.