ORIGINAL: GeraldO
The speed of the motor is regulated by 'chopping' the current (turning it on-off rapidly) at part throttle. With the current being chopped the average torque is reduced so it spins the load slower. The ESC will detect the loaded RPM and adjust the phase switching timing to match.
That's true, but I guess that the max rpm is limited by the 3-phase's frequency and the number of poles.
The max rpm = 2 x frequency x 60/number of poles