How to change the FFT phase domain of each frame by 90 degrees I have read a signal in Matlab, resampled and implemented an FFT of each frame on it, now I want to rotate the domain of phase in each frame 90 degrees.

I have a vector of FFT and used the function named rot90(matrix), that rotates a matrix 90 degrees, but I'm not sure it is what I wanted to work correctly on my function.

How can I do that in some other way?  Or does the rot90 correctly work on changing the phase of domain in FFT which has been imported into a vector?
It sounds like you're trying to plot the FFT such that the result is centered at 0, instead of at Fs. Matlab has a function for this fftshift.

Here's a simple example when trying to plot either the onesided or twosided FFT.

f = 100; % Signal frequency (Hz)
fs = 1024; % Sampling frequency (Hz)
N = 1024; % Number of samples
Nfft = 1024; % FFT size

xf = 20*log10(abs(fft(x, Nfft))); % Compute the PSD

fw1 = fs * (0:Nfft/2)./Nfft; % Onesided domain
fw2 = fs * (-Nfft/2:Nfft/2-1)./Nfft; % Twosided domain

figure
subplot(211), plot(fw1, xf(1:Nfft/2+1)), title('Onesided')
subplot(212), plot(fw2, fftshift(xf)), title('Twosided')