@Nurki
If you have NOT migrated your Nest Account to a Google Account and wish to change the phone number you use for 2-step verification/2-factor authentication:
"If you plan to get a new phone number and stop using your old one, you should turn off 2-Step Verification before you deactivate your old line. Then you can turn 2-Step Verification back on with your new number."
https://support.google.com/googlenest/answer/9295081?hl=en-AU&sjid=2593032938270148643-NC#zippy=%2Cc...
If you have a Google Account, see the page below. You'll have to change the phone number there while you still have your old phone number.
https://support.google.com/accounts/answer/3463280
