The rule is quite clear in that "Learner and provisional P1 drivers must not use any function of a mobile phone while driving or when the ignition is on."
Also worth noting the "ignition on". The car must be parked and off.
A GPS device that is not a mobile phone is permitted for all drivers, as long as the device is secured in a mounting fixed to the vehicle and does not obscure the driver’s view of the road. The device must not be placed in a location that will increase the likelihood of injury in a crash.
For more information go to Know The Rules.