About phase imaging LINK: http://www.bruker.jp/axs/nano/imgs/pdf/AN011.pdf
According to question it maybe possible to see differences of phases in your material. Maybe another than PI mode should be used. Once upon the time I was using EFM to find small carbon contamination in carbon (diamond) material. Some techniques of Ion beam microscope (FIB) let to see differences in grain orientation, so maybe in phase differences contrast will be visible (?).