This wikiHow teaches you how to remove a secondary phone number from your Apple ID account on an iPhone.
Steps

Step 1. Open your iPhone's settings
This is a gray gear app located on one of your home screens.
- This app can also be in a folder labeled Utilities to stand.

Step #2. Scroll down and tap on iCloud
This can be found in the fourth group of menu options.

Step #3. Tap on your Apple ID email address
This is at the top of your screen.

Step 4. Sign in with your Apple ID if prompted

Step 5. Tap on Contact Information
This is the first option listed under your Apple ID.

Step 6. Tap the phone number you want to delete

Step 7. Tap on Delete Phone Number
Note: You cannot delete a phone number with the addition "Primary" next to it. "Primary" means the number is your only Apple ID phone number stored in your account

Step 8. Tap on Uninstall
Your friends can no longer use this phone number to communicate with you through Apple services such as FaceTime, iMessage, and iCloud Share.