There are a lot of mounting instructions here on Orchid Board. You can find them with the search function. I write this because different people do it differently. Here is a thread I wrote on how I do it:
Mounting Oncidium sphacelatum, a climber, Part 1
I use fishing line or dental floss for tying plants to mounts. For a Phal, I would first tie a thin layer of wet sphagnum moss to the mount, and tie off the twine. Then I would tie the plant over the moss, with a new piece of twine.
Mount it so the two ranks of leaves are generally going off to the right and left sides, with the sharp point of the newest leaf pointing downward. This is how they would grow in habitat. If your plant hasn't been moved around much as it grew, the leaves will probably lean all in one direction, with their little points pointing the way the plant leans. It should be mounted so the leaves lean downwards.
Try to tie some of the roots so they are touching the moss, but don't cut them with the twine.
In the future, go to a hardware store and buy a piece of untreated cedar fence plank. You can use a hacksaw to cut off whatever length you wish. One piece of fencing may cost less than what you spent on the piece you bought.