This is a bug that has been brought up several times. Even when not dithering, SGP sends a settle command to PHD2 between frames. It shouldn’t do that. It is a completely unnecessary waste of precious imaging time and is a legitimate bug that the developers should fix.
Edit: Just found this thread from a couple of years ago:
It appears that this is expected behavior. I encourage the developers to reconsider, or at least allow the option for the user to select settling when there is no dithering. I can only think of one reason that guiding would be disturbed (DSLR mirror movement) between frames, and that doesn’t seem likely. On the other hand, the unwanted settling overhead when not dithering is a large, tangible disadvantage.
Tim