You may have already checked the Help item from the PHD2 top menu, but if not here is a section of Help Trouble Shooting Section that covers the problem-- (emphasis added)
Calibration and Mount Control Problems
If you are just starting to use PHD2 or are connecting to new equipment for the first time, you may have trouble getting calibration done. This problem usually takes one of two forms, each requiring different responses:
1.
The star moves during calibration but it moves "too far" or "too little." If you've used the new-profile wizard and have provided correct values for focal length, camera pixel-size, and mount guide speed setting, the "step-size" used in calibration should already be correct. But if you've configured your profile by hand or have changed guide speed settings in the mount, you may need to adjust the 'calibration step-size' parameter in the 'Guiding' tab of Advanced Settings. The help content there describes how this parameter is used, and you should be able to resolve the problem quickly. But if you've used the new profile wizard and are seeing problems with "too far" or "too little" guide star movement, the problem probably lies elsewhere.
2.
The star doesn't move enough during RA calibration, declination ('Dec') backlash clearing, or Dec calibration. These problems are announced by alert messages at the top of the display window. With longer focal lengths, small movements may even be the result of seeing deflections, and the mount isn't really moving at all. Dealing with this sort of problem is described next.
In nearly all cases, the "no movement" problem is caused by failures in the mount or in the cabling and connections. The best tool for trouble-shooting this is the 'Manual Guide' option under the 'Tools' menu, as described in the Tools section of this help document. Simply use the directional controls in the 'Manual Guide' window to send commands directly to the mount while watching a star in the image display window. Use fairly large guide pulse amounts - at least several seconds - so you can clearly see if the mount is moving. Try to move the mount in all four directions and verify the target star is moving by roughly equal amounts. If the mount does not respond, you know you have either hardware or connectivity problems to resolve - nothing to do with PHD2. If you're using a Shoestring device to connect to the mount, watch its indicator lights to see if the commands are reaching it. Similarly, your ST-4 compatible guide camera may have indicator lights to show when guide commands are being received. If you're using an ASCOM connection to the mount, be sure the COM port assignments are correct. You can also use some of the ASCOM-supplied tools like POTH to be sure the ASCOM driver is communicating correctly with the mount. It is best to use the latest version of the ASCOM driver for your mount because older versions of these drivers might have bugs associated with pulse-guiding.
