Open the Agenda or one of the Schedulers in the calendar icon in the main menu.
Right click (or hold, on the tablet) on the hire duty in the Agenda, or on a segment of the Scheduler. Choose the option Phone details.
A window shoes you all of the available telephone numbers, or no available contacts if there there are none specified in the data of the driver.
For a driver assigned by a supplier, it is possible to only view the contact information that he has specified as Public.