I'm not saying there is no way to specifically encourage root growth, but I don't know of it. Of course, you do the obvious in taking care of your plant to provide for its needs. But my phals decide for themselves when they will grow new roots, or leaves, or spikes. Often, a plant in its first year at my house will sit and just think about it. Finally I will see a new root, or the beginnings of a new leaf.
I think if I lived in a more tropical area, they would grow more quickly. But I don't. And they eventually do just fine.