The iPhone was lost along with the number that was linked to iCloud.
The iPhone was lost along with the number that was linked to iCloud. Now I can't restore access to my account. How can I change my phone number?
Apple Watch Series 4, watchOS 8
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You can also receive the code for the Tow-Factor Authentication on a different trusted device or phone number:
Get a verification code and sign in with two-factor authentication - Apple Support
If this is not possible, using the Account Recovery process would be the next step:
How to use account recovery when you can’t reset your Apple ID password - Apple Support