Only you can see this information.*
Only community members who you have added as a connection will be able to see this.
You may want to use this with hybrid communities that have an internal and external component. This way you can show your phone number to contacts, but not to your broader customer base.
All members of your community can see this.
In public facing communities, like a customer support centre, anyone can see this information, including anonymous users.
* System administrators have access to any account information