Trusted phone number

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 your trusted phone numbers use one of these methods:

● On your 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 your 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 .

If you find you can’t sign in, reset your password, or receive verification codes, you can request account recovery ( How to use account recovery when you can’t reset your Apple ID password - Apple Support ) to regain access to your account. Account recovery might take a few days or longer, depending on the specific account information you can provide to verify your identity.