When you register a website on your own, you have to supply your contact data, including phone and email.
These will be immediately abused by numerous people who want to improve your website, sell you an insurance and inform you about a rich Nigerian princess who wants to send you her money.
Receiving similar messages by email is usually not a problem: you can just classify them as "spam"; with phone it is going to be more complicated: the National Do Not Call Registry apparently does not really protect even private phones. (And it says it is not going to protect business phone numbers at all.)
The problem is resolved by Privacy Protection provided by most hosters: for extra fee they will publish their contact data instead of yours.
We believe that Privacy Protection is necessary so it is included in our hosting service. By default we protect only your phone number: we will publish our contact phone number, but your name, mail address and email.