If you are dumb enough to do it, and it is usually optional, then you have no control over what companies use that number for and there is a real possiblityy that companies will use that phone number, either for their own marketing purposes or sell it to someone else.
Clearly the fruity cargo cult Apple had never thought of doing something that despicable and is now thinking “I’ll be having some of that”.
With the upcoming releases of iOS 11 and macOS High Sierra later this year, Apple is planning to force many users to adopt two-factor authentication for their accounts.
The company this week sent an email to customers who have the existing two-step verification enabled for their Apple IDs, informing them that once they install the public betas of the new operating systems they will be migrated to two-factor authentication automatically.
Two-step verification is an older method of account security that Apple rolled out before full two-factor authentication was available. Apple is phasing that out and will be upgrading people with eligible devices automatically.
"Once updated, you'll get the same extra layer of security you enjoy with two-step verification today, but with an even better user experience. Verification codes will be displayed on your trusted devices automatically whenever you sign in, and you will no longer need to keep a printed recovery key to make sure you can reset a forgotten password," the email from Apple says.