Compare phase and magnitude spectrum results of 2 Images
When you create the transform, an embedded assumption is that you extend your image to infinity by duplicating it vertical and horizontal direction.
Each point in the transform provides information about a 1D wave (frequency that has certain direction based on the point location and phase (how it is moved along the image).
Try to draw a 1D sine wave over a 2D array and then run the 2D FFT to see how the point is created - the higher the frequency the point further from the origin. Starting at a peak will result a $90^0$ phase...