Any AC signal can be expressed as a phasor. The phasor equation has two components, one real and one imaginary. For example, an AC voltage signal with amplitude of $V_m$ can be expressed as a phasor arrow (as shown above).
The x and y components of the phasor are: $$x = V_m cos(\phi) \\ y = V_m sin(\phi) $$ Thus the phasor itself can be expressed as:
$r = V_m (cos (\phi) + j \, sin (\phi)) = V_m cos (\phi) + j V_m sin (\phi)$