I have a Phalaenopsis standing in a pot which is in another pot. The orchid pot sits on a brick to raise it above the water that drains through after being watered. Some of the roots have grown over the side of their pot and extend down to have their tips in water thta is about 1 inch(2.5cms) deep in the outer pot. They are over a foot(30 cms) long. Is this a good thing to allow or should I direct the roots over the edge of the outer pot?
It sounds like your plant has a healthy root system. I would just let the roots grow where they want. In my semi-hydro pots the Phal roots grow right down into the water reservoir and suffer no ill effects from it. If the roots have grown in the water for a while you could suffer root die-back as a result of removing them from the water.
I think that this system sounds good as long as you monitor the roots, checking for any brown that should be trimmed off. My Phals are on the ledge next to my shower and it's fun to watch the roots turn green as the humidity rises!