Question
The stem, holding about 10 blooms turned from green to pinkish brown
and the blooms withered all at one time and fell. What happened?
I have about 15 plants and this has never happened before.

Answer
Mary, you are right that this is unusual.  Usually, flowers will fade in the same sequence in which they open (so, first to open should be first to close).  Loss of all flowers at once is usually the result of trauma to the plant such as exposure to the cold or some other stressor.  I suspect that your phalaenopsis is one whose flower spike naturally dies back after flowering (some hybrid flower spikes actually remain green and may flower from the same flower spike).  This particular plant may be one that is genetically programmed to lose its flower spike after each flowering. If this particular plant has bloomed for you before and did not behave this way, then, trauma is the most likely explanantion.  Otherwise, I suspect that genetics plays an important role.