Howdy lei24,
The information outlined below details how to go about changing the phone number used to obtain a Verification Code.
- Make sure that you have a strong cellular network connection on your phone.
- Make sure that your phone number can get SMS messages. To check, ask someone to send you a text message.
- Make sure that the correct phone number is associated with your account:
- On your iPhone, iPad, or iPod touch, tap Settings > iCloud > Keychain > Advanced. (In iOS 7, tap Settings > iCloud > Account > Keychain.) Make sure the phone number under Verification Number is correct. If not, enter another phone number.
- On your Mac, choose Apple menu > System Preferences. Click iCloud, then click Options next to Keychain. (In OS X Mavericks or earlier, click iCloud, then click Account Details.) Make sure the phone number under Verification number is correct. If not, enter another phone number.
If you can't access a device that has iCloud Keychain enabled, contact Apple Support and verify your identity to get help setting up iCloud Keychain.
Get help using iCloud Keychain
https://support.apple.com/en-us/HT203783
All my best,
Allen