Use the abs (magnitude) and angle (radian phase angle) functions.
The phasor notation for it would be:
phasor = [abs(z) angle(z)]
However you cannot calculate anything until you resolve the problem:
z = (10<-50)*(-7+j10) / -12*exp(-j45*(8-j12))
↑ ← HERE
That is not valid MATLAB code. (I also corrected the ‘e^’ notation for the exponential function.)
(Another problem is ‘j10’, ‘j45’ and ‘j12’. I am not certain what they are, however using numbered variables such as these is generally considered poor programming practice. Put them in a vector and reference them as elements of the vector.)