Two factor authentication for a phone number that's no longer available

Viequé wrote:

Followed instructions on my Imac and added his new phone # to my trusted devices on my Imac by using the call method.

You need to add his phone number to his list of trusted numbers, not to yours.

If he can still sign into his account on another device he can investigate adding more ways to get a code such as multiple telephone numbers where you can receive a text or a phone call. This is from the section "About trusted phone numbers and trusted devices" in the article: Two-factor authentication for Apple ID - Apple Support

To see, add, or change trusted phone numbers use one of these methods:

● On his iPhone, iPad, or iPod touch: Go to Settings > your name > Password & Security. Next to Trusted Phone Number, tap Edit.

● On a Mac computer choose Apple menu  > System Settings (or System Preferences), then click his name (or Apple ID). Click Password & Security, then add or remove a trusted phone number.

● Using a web browser: Go to the Account Security section of https://appleid.apple.com .

Similar information for the iPhone can be found here --> Manage two-factor authentication for your Apple ID from iPhone - Apple Support

If he had set up an Account Recovery Contact ( Set up an account recovery contact - Apple Support ) he can also get a code that way.

If he can’t sign in, access a trusted device, reset your password, or receive verification codes, he can request account recovery to regain access to his account. This article explains how to recover an Apple ID after a waiting period - How to use account recovery when you can’t reset your Apple ID password - Apple Support

You may also wish to read the articles 'Two-factor authentication for Apple ID' ( Two-factor authentication for Apple ID - Apple Support ) and 'Get a verification code and sign in with two-factor authentication' ( Get a verification code and sign in with two-factor authentication - Apple Support ). Various sections contain information that is useful in understanding about the trusted devices (an iPhone, iPad, or Mac that Apple knows is yours) system, and how to get a verification code on a trusted device or at a telephone number.

Try this: get support and assistance from Apple directly, see  -> Contact Apple for help with Apple ID account security -> Contact Apple for help with Apple ID account security - Apple Support