how to make fft ignore phase shift when only interested in magnitude
You can't make an FFT ignore phase (for strictly real input), except for signals which have frequencies that are exactly periodic in the FFT window length.

Otherwise, you will have to interpolate to get any between bin magnitude peaks.  And an accurate magnitude interpolation of any non-bin-centered frequency will depend on phase (easiest if you reference phase to the center of the data window), especially near the DC or Fs/2 bins, but to a much smaller extent, thru the rest of the FFT result as well.