What is phaser quantity

A sinusoidal alternating voltage or current is represented by a line OA, whose length is proportional to its maximum value. This is known as a phasor. It is assumed to rotate in the positive direction i.e. CCW with an angular velocity ω

When the phasor OA is along the X-axis( reference) the voltage or current is at it’s minimum i.e. the zero value. As the phasor rotates through an angle θ from its reference position in the CCW direction, the magnitude of the voltage or current increases to C1 at a phase θ corresponding to point C and reaches a maximum at D1 at phase
θ = 90°corresponding to point D. OA is projected as OC on the y-axis, which corresponds to C1, and the OB projected along x-axis corresponds to q on the waveform. Similarly other pair of points can be generated as the phasor advances in the CCW direction and completes one rotation.
In general,

OC = OA sin θ
v = Vm sin θ
when θ = 90°,v= Vm point D1
when θ = 180°,v= zero point E1