How to change my phone number to receive verification code for key chain ?

help pls...

1. On your iPhone, go to Settings → iCloud → Keychain and switch Keychain off then on again.
2. Tap "Approve with Security Code", tap "Forgot Code" and then tap "Reset".
3. Follow the instructions to reset iCloud keychain and create a new passcode.
   You will then be prompted to update to your new number.

if that does not work, try to log in to https://appleid.apple.com/ and you will be able to change under Phone Numbers.

🙂