Unless you removed the slip joints and changed their positions, it won't matter a lot how you put it back together, assuming the assembly was balanced. If you can identify the three sections and put them back in the same locations, it should be OK. Yes, the u-joints can be assembled rotated 180 degrees from their original positions, but that's not what phasing is. Phasing is the angles between the u-joint yokes on the same section of driveshaft. Typically an in phase section would have the axis of the yokes in the same plane and as I mentioned, the only way to change that is by installing the slip joint incorrectly on a section. Many times that's impossible because of a spline that's keyed to only go together one way.
