If you have been configured as a system phone user by the system administrator, then you can also add, edit and delete some external directory contacts.

This only applies to external directory contacts entered locally into configuration of the telephone system to which you are logged in.
External directory contacts imported by the system from other sources cannot be edited. However, if a local entry is created with the same name or number as an imported entry, the imported entry is discarded in favour of the local one.