I'm not sure this would work; the phone will introduce a delay in the feedback, and this can be bad, and also, the sensors need to be placed in fixed positions

I'm not sure this would work; the phone will introduce a delay in the feedback, and this can be bad, and also, the sensors need to be placed in fixed positions for the best response (the gyro is usually placed right in the center). Also, petrol/nitro engines are not the best for this kind of job, as it needs a very fast response in rotation speed and fuel engines have a high latency. What you can do is use a fuel engine as an electrical power generator or use variable-pitch propellers to get a faster response.