Re: 480 ,4 wire yellow, brown, orange
You can determine "A" phase, if that is the POCO's nomenclature and not 1, 2, 3, 4, 5 or 6, using a phase angle meter or an oscilliscope. However, you would still need to have a Known Point to establish a reference. The only time that I can think of when you must ensure that two sources are in phase is when you want to parallel them. If you are not paralleling than it is usually sufficient to just know the rotation.
When are some other times when it is important to ensure that two sources/conductors are in phase?