# Interpreting Nyquist Plot for Phase and Gain Margins

I have an open-loop system transfer function given by $$G(s) = \frac{K(ABs^2+As+1)(Cs+1)}{s^2A(s(C+D)+1)}$$ so I'd expect two poles at the origin and one at $$s=\frac{-1}{C+D}$$. After using Matlab to obtain the Nyquist plot (seen below), I'm having some trouble interpreting it. Matlab states that the phase margin is 16.2 degrees. What does this mean exactly? How does changing this phase cause encircling of the -1 point? Also, I've seen examples of how to interpret gain margin from nyquist plots, but I'm not quite sure how to determine this with a root at the origin.

Any clarification would be greatly appreciated.