I discuss the route for suppression of chaos in nonlinear oscillations by phase modulation. I consider the Duffing oscillator forced with phase modulated sinusoidal force. Applying a simple averaging technique, show that the phenomenon of chaos suppression due to reshaping of the driving force may be easily explained as an effect solely arising from the change of the effective amplitude of the first harmonic in the Fourier series expansion of the driving force. This conclusion is clearly confirmed by numerical simulations.
