The Optiwave 3D viewer which opens does give you 4 views.
1. Top-Left: A top down view of the DFT of the field, in your case the EZ field, as captured by your observation area. The z coordinate is in fact the real/imaginary/amplitude value depending on what you have selected. This view has a red marker which can be moved using the mouse. This cross hair is used to define the other views.
2. Top-Right: The DFT values along the vertical part of the aforementioned marker are shown in this view. This is the X-cut view .
3. Bottom-Left: The DFT values along the horizontal part of the aforementioned marker are shown in this view. This is the Y-cut view.
4. Bottom-Right: The 3D representation of the data.
The field exported from an observation area is a DFT which has real and imaginary components. The amplitude and phase are the standard definitions for a complex quantity. amplitude = sqrt(real^2+imaginary^2), phase = atan(imaginary/real).