Hello! @gregjames
Welcome to the LastPass Community.
Unfortunately, it is not possible to add a second phone number as a recovery method for your MFA, but you can enable a second MFA, meaning you can set the LastPass MFA and the Google or Microsoft MFA in a second phone. You can also set the primary MFA method.
Please access your vault, go to account settings, Multifactor options, then choose another option from the list.
Please let me know if you need additional help.
Greetings!
Verlaine | Customer Care