PHD2 automatically applies a stretch to the displayed image. If the gamma slider is to the far right and there is insufficient light (very short exposure), the stretch will result in a speckled pattern (see attached 2ms.jpg). OTOH, with the slider to the right and there is too much light (long exposure), then the image will be smooth (see attached 15s.jpg).
You can play around with the exposure, however, you may never get an image in daylight that answers the question 'is the camera working in PHD2?" That may be a night time only test.
Bryan