Took out my Passporter guidebook to look. According to the map, it's outside the main entrance to POR. It's a little ways down on the right. This is the bus stop we used when we stayed there. It's the first stop at POR, they pick up at POFQ first.
I just double-checked my map of POR. Buz is correct. The south bus stop is actually the Mason-Dixon Platform. We also used it on our last stay and we were in Magnolia Terrace. Just stopped at the food court for coffee and then on to the bus stop! It worked very well for us too.