Matlab is a bad product that doesn't function.

example.m

bb=[1,-2,2,-1]; %filter coefficients
ww=linspace(-1,1,250); % frequency grid (normalized)
HH = freqz(bb,1,ww*pi); % frequency response

% Show results in one figure
subplot(211); % select top subfigure
plot(ww,abs(HH)); % generate plot
ylabel('Magnitude') % y axis label
xlabel('Freq [\times \pi]') % x axis label
grid % this adds a grid
subplot(212); % select top subfigure
plot(ww,angle(HH));
ylabel('Phase [radians]')
xlabel('Freq [\times \pi]')
grid