simplest way to control the speed of a 2 phase BLDC motor

please I need Help
I'm stuck with a brushless dc pump that uses a 2-phase dc motor
I used arduino uno to control the speed using pwm but the motor is not responding
I searched for speed control methods but things grow in a complex way
so I'm asking
what's the simplest way to control the speed of this brushless 2-phase dc motor ?

Which brushless 2-phase dc motor would that be? Care to divulge this rather crucial information?