Let's say I have a LTI system described by following transfer function $$G(s) = \frac{(s+1)}{s(\frac{s}{10} - 1)}.$$ As soon as I run following Matlab code
s = tf('s');
G = (s + 1)/(s*(s/10 - 1));
bode(G);
I receive following Bode plot
The magnitude part is in accordance with my expectation (rough sketch created by hand). As far as the phase part there is a discrepancy between what Matlab gave me and what I expected. Namely I expected that until the first break point $\omega = 1\,rad\cdot s^{-1}$ the phase should be $-90^{\circ}$ due to the pole at the origin. It seems to me that there a phase shift of $-180^{\circ}$ but I don't understand why.