This question has been asked a million times, controlling robots with phones and calculators.
The reality is that you don't want to cut steel with a pocket knife. Use the right tool for the right job.
A microcontroller has tons of I/O such as PWM and ADC and I2C thats perfect for controlling robots . . . a camera or a calculator has none of that.
Plus, a microcontroller (non-augmented) costs like $3!
That being said, those who did get a camera to control their robot (google for them) still had to use a microcontroller as an interface.