Flight crew fails to answer the call

You know how you are reminded to turn your mobile phone off before take-off? Well it appears that the one person on a recent Thomsonfly service from the UK's Robin Hood Doncaster Sheffield Airport who failed to follow those instructions was the pilot. Passengers on the aircraft, which should have been heading for Tenerife, were told by the embarrassed captain that they could not take off until he he had found his mislaid mobile phone, which was switched on.
After sitting on the runway for an hour, they had to disembark and wait for a replacement aircraft and crew.
Why didn't the pilot simply call his own mobile from another phone and listen for the ringtone to reveal its whereabouts? Apparently it was in silent mode.
Thomsonfly insists this is a very rare occurrence, but points out that all mobile phones must be switched off during flight for safety reasons and this applies equally to the flight crew's own equipment.
The phone later turned up on board the aircraft.