Hello OB people

! It has been such a pleasure to find this site, as its truely helped me get going with my new orchid passion.
I really want to switch over my phal's when the last blooms falls off. I'm concerned a little about the media they are in now, but they seem to be doing ok for now. I've read here several times to wait until you see new root growth before repotting in S/H.
My question is, what is the best way to find out if there is new root growth without unpotting the plant. It's in a clear container, but the media is dark, and aside from the green roots, that's all I can see? Should I look for new aerial growth, or is there a good quick way. Also, how long should the new roots be? I figure the shorter the better. Just can't wait to get them in new, and better, homes, but dont want to kill them. Thanks all!