The phone book is shared between all users on your account. You may click on a number to call it directly or use the SMS icon to send a new message. If an incoming number matches an entry in the phone book, the contact's name will be displayed automatically on your handset, in addition to their number.
To access the phone book, open the extension then click the phone book icon in the navigation bar:
To add a new entry click on add:
Enter a contact name, number and (optional) speed dial, then click "Save".
Once added the entry should be shown in your phone book as below.
You may edit an entry by clicking the "pencil" icon to the right of the chosen contact. From here, you may modify the entry or click "Delete" to remove it from the phone book.