how to do complex calculation?invoving Iota and phase eg: phase of 4+9i

The 1.1526 is correct to 4 decimal places.

So the phase of this complex number is the angle $$tan^{-1}\left(\frac{9}{4}\right)\;\approx\; 1.1526$$

My knowledge of complex numbers is very rusty but I think all of this is correct.