Generally, the reasons for a phone number are:
Account recovery 2FA
If you don’t want to use your number then consider a pre-pay sim. Depending what country you are in this will cost pennies per year.
I would suggest something like ProtonMail or most paid email services won’t require a number.
I don’t remember the last time I used a phone book. There have been better ways to get a number for a long time.
Think it must be at least 30years ago.