I think your choice depends alot on how far down the windspeed spectrum you want to
If you simply aren't going to sail in < 7knots of wind, then either board would be good with a slight advantage to the Phantom as it planes a bit more like a short board than the Kona.
If you are going to be sailing in < 7 knots, then the longer waterline length of the Kona gets the advantage.
If you are thinking of racing, then the Kona Fleet is the way to go.
The Kona is really big, the Phantom is not quite so big.
Hope this helps,