Victoria- Are you familiar with orchidspecies.com also known as IOSPE? It is a great site for orchid info of species only. Phal tetraspis is a species orchid.
Here is a link for it:
Likes even watering year round. So I would water when the roots look whitish. WHen watered they will turn green. And don't need any more water as long as they are green. Wait until they are whitish in color.