Many of the Google account users want the phone number to fix their problems as not all users are well informed to get this information by themselves. Millions of accounts are opened over the Internet every day, with multiple users using multiple accounts. It is a bit difficult for users to close their accounts with email id and password, manage the hacked accounts and the problems they face while changing the password. Now you don't need to think about it, as the company takes care of all customers.
https://sites.google.com/view/googl-help-center