Electrical Engineering - Alternating Current and Voltage - Discussion

A phasor is a straight line drawn in such a way that its length is related to the amplitude of the sine wave represented, and its angular position relative to other phasors is related to the phase difference between the quantities.

Note that:

a. At any point in time, the length of the red dotted line represents the instantaneous value of the wave.
b. The length of the phasor represents the amplitude of the wave.
c. The angle of the phasor gives the phase of the waveform. Increments in phasor angle in the circular diagram are equivalent to time or angle increments along the horizontal axis of the waveform diagram. So with this addition of angular information, the phasor gives a relatively simple way to show the complex relationships that exist between sine waves in an AC circuit.

As per definition amplitude means the peak value or maximum value of any signal, whereas the length of the phasor represents the rms value of signal. So as per my opinion the answer given above must be explained again, or it must be looked again for explanation.