phase difference 2 signals.

In principle it should work. in terms of resolution it depends...

You can think of the idea in simple time domain terms as follows:

your ref is: sin = 0,1,0,-1, cos = 1,0,-1,0

if your signal is exactly in phase with sin then you get:

Re = 0,1,0,1, im = 0 i.e. double frequency (120) plus dc

if your signal is exactly in phase with cos then you get:

Re = 0, im = 1,0,1,0

if your signal is in between then you get a value indicating where it is in phase.

As regard amplitude, the same applies in relative sense to sin/cos amplitude.

To read the phase you can either compare the vertical components (Re/Im) directly or have an LUT to convert to degrees.