Hi Iris, if the roots are dry enough then it may not be the water. Inspect the plant more carefully, as I suspect an insect may have gotten into the plant. I had a Phal which was robust with flowers and suddenly the flowers started to wilt. After careful examination there was a medium size cockroach in the plant which may have been disturbing the system for its flowers the prematurely drop. The leaves are also drooping in contrast to a healthy Phal. which will have its leaves upright.
Also, try taking out the plant from the plastic pot and see if the roots are wet in the center as the medium (are they wood chips) may have stayed wet at the inner part of the roots.
You may also have to cut the stem, so as to let the plant focus on healing as you do the above.