verification phone number is wrong in my iCloud account

The second section of this support article, step 3 explains what you need to do to change or validate your Verification phone number for Keychain:

If you didn't receive the verification code via SMS

1. Make sure that you have a strong cellular network connection on your phone.
2. Make sure that your phone number can get SMS messages. To check, ask someone to send you a text message.
3. Make sure that the correct phone number is associated with your account:
   • On your iPhone, iPad, or iPod touch, tap Settings > iCloud > Keychain > Advanced. 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.

Here is the entire article FYI: Get help using iCloud Keychain - Apple Support

Cheers,

GB