You can use freqz() if you want, Because filt() returns a tf object from the Control System Toolbox, bode() or bodeplot() functions in that toolbox can also be used
num = [1 2];
den = [1 2 3 4];
sys = filt(num,den);
w = logspace(-2,pi,100);
[m,p] = bode(sys,w);
figure
subplot(211);
semilogx(w,db(squeeze(m)));
subplot(212)
semilogx(w,180/pi*angle(exp(1j*squeeze(p*pi/180))))
h = freqz(sys.num{:},sys.den{:},w);
figure;
subplot(211);
semilogx(w,db(abs(h)));
subplot(212);
semilogx(w,angle(h)*180/pi)
