Phone number listings are accessible to the public unless the owner chooses to utilize services to protect the privacy of a phone number. There are ways to have the number unlisted, unpublished or blocked.
The owner may request that a phone number remain unlisted, which means it's not available in a public phone directory. An unlisted phone number, also referred to as private, may still be shared or sold. A phone number can also be unpublished at the request of the owner, which means that it's both unlisted and also not available for sale or sharing.
A phone number is blocked by either requesting per-line blocking or per-call blocking. Per-line blocking prevents the phone number from appearing on caller ID on all calls made from that number. With the per-call blocking option, the user must dial a code prior to making an outgoing call in order to activate the block. Both options can be set up with the phone company.