You don’t have to replace the phone with your right hand to twist it. The natural way to pass the phone between hands as you take a call is by keeping the receiver ‘facing’ you. If you kept passing between hands this way each 180 degree twist as you change hands would be negated by a -180 degree as you pass it back.
However, if you pass it back to your left as you hang up, the natural thing to do is to twist the receiver away from you, in preparation to placing it face down. Rather than being a -180 degree twist this is another 180 in the same direction. Thus your call has produced a 360 degree twist.
If you were really smart (or pointlessly anal with nothing better to do :)) you could use the twists to keep count of the number of calls you’ve taken.