Hi,
I looked extensively for a PHD when I had my 2305. In the end, there was no good solution due to the limited cat 1 3pt hitch. More specifically, it's the lack of ground clearance or height.
Granted, i was looking for something that could get down 4 ft, below our local frost line, for putting in some footings. If you don't need to get that deep, you may be able to find something that will work for you, more like 3 feet deep. It would be helpful to say how deep and maybe what diameter you need to go.
For my needs, I ended up using my 260 backhoe. Even though it upset more soil, it was much faster in our rocky new england earth than any PHD would have been.
Hope this helps