The term "phasing" in terms of driveshaft nomenclature is not the correct word for the alignment issue you are asking about. Phasing refers to the orientation or clocking of u-joints in relation to each other on a given driveline.
Combining several simple mechanical properties/functions together into one system with multiple affective parameters seems to be the root of the great amount of confusion and misunderstanding surrounding pinion angles and ideal driveline construction and set-up.
Dr Diff, helped me get a basic understanding of what's going on with this topic, but I still lose my perspective sometimes. These attachments help me keep it simple.
There is a great video showing the affects of u-joint positioning and the slight increase and decrease of driveshaft speed that result as the u-joints are brought into and out of the elliptical movement patterns by changing their working angles.
Ideally, u-joints work best when installed between two parallel lines that are offset from each. They require a certain amount of offset from parallel to work properly. That amount is described on one of the manufacturers websites tech pages.
Because our drivelines are not fixed in position due to engine torque, suspension movement and other factors, initial settings such as pinion angle are a compromise to get the components aligned within an acceptable range or sweet spot.
