Hi @IMI
It is not possible to restrict access to the Phonebook for an extension, as the phonebook is available globally.
The only alternative is to choose which extensions to not be shown in the company phonebook.
This can be done by enabling the option "Hide this extension from 3CX company phonebook and 3CX Apps" under the Options tab of the extension.
I think they are working on phonebook retriction option in V20.
Quote the 3CX Reloaded - V20!
Groups Become Departments and Powerful
A big part of V20 are the new Departments. Departments replace Groups as it more accurately represents what they are. In Windows Active Directory these departments would be called Organizational Units. These departments are now much more powerful - they can have their own office hours, holidays, time zone and language settings. Soon they will also have their own phonebook and CRM configuration amongst other things.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.