Difference between the Magnitude and the Phase Spectrum of the Fourier Transform?
Fourier Transform changes basis from time (spatial data) to frequency. To encode frequency we need amplitude (magnitude) to know how strong is signal at given frequency and phase to know when sine started - in what moment of its phase we are now.

Example: take input signal $5\sin(x + \pi)$, here phase is $\pi$ and magnitude is $5$.