Hi! most of my orchids are phals, but the first ones I bought in May 2010 are just starting to show new roots and leaves. So, it seems like they took a sabbatical, hehe!!
All my new ones are doing a lot better since I started using pots that have just enough space for the roots. My mistake was, that I was choosing a plastic pot to fit inside a clay pot and not the best one for the root size! Providing warmth and humidity around them can also help a lot to encourage new growth. Right now I have 4 phals that had no roots inside of what I call my version of 'spag and bag' and 2 of them have big roots, even one of them is growing something that looks like a flower spike. (I think!)
So, now every time I repot, I also use a humidity tray and cover the whole thing with a clear plastic bag and its working very good for me!