Chosing correct frequency axes.

Hi all, I want to have amplitude and phase reconstruction of the signal. My signal is having 40KHz bandwidth and starting frequency is 70Khz to 110 KHz. Suppose my signal is x.

nfft = length(x);
res = fft(x,nfft)/ nfft;                     % normalizing the fft
f = fs/2*linspace(0,1,nfft/2+1);                  % choosing correct frequency 
res = res(1:nfft/2+1);                            % amplitude of fft
res2 = fft(res);

now i want to plot frequncy versus amplitude and frequency versus phase. figure, plot(f,abs(res2) where the amplitude shoud be lying from the 70KHz to 110 Khz and same in the Figure(f,angle(res2), the phase shoud be spreaded over 70kHz to 110Khz. So how to chose the correct frequency axes.