P2 gimbal control never worked. After getting no response back from DJI, I found others with the same problem.
I had to save my investment in DJI and after much research, the solution was a new Futaba T10J Heli TX.
If you have done the same please let me know so we can share setting info.

First bind the Phantom with the transmitter.
Then select a channel to control the gimbal movement.
You can refer to the Futaba user manual for detailed step.