PHASE function
Description
PHASE(A) returns the phase angle (or angular component) of the complex number A, expressed in radians. This is Excel's IMARGUMENT function. $$ phase(a+bi) = asin\left(b / abs(a+bi) \right) $$
Visual representation
Example
PHASE(2+3i) returns 0.982793723
PHASE(pi()*1i) returns 1.570796327
PHASE(3) returns 0.