A general transfer function can be represented in the following way:
Bode plot is a plot of 
and
the 
versus 
. It is a semilog plot
where the x-axis is the log-axis and the y-axis is the linear axis.
Since 
and also phase of the product of two
complex numbers is the sum of their phases we can plot the Bode plot of
each factor separately and then just add them up. For this reason we look
at the Bode plot of each factor separately.