always phi (mod 360)
and I mean the "real" mod - C++ thinks that it's funny to return negative modulo because a fast answer that's wrong is better
than a good answer that took a nanosecond longer:

usually phi [2 pi] gives an angle between 0 <= phi < 2 pi

however, in C++, the % operator is actually a "reminder" operator, so negative values are fine which means that I have to mod
twice just in case it was negative.