Hi- I am fairly new to orchids and phals. I have one that all but 3 blooms dropped off 3 weeks ago at least and seem to be lasting forever. Certainly I don't mind this, but wonder why this is happening. Blooms above and below them on the same spike have dropped. Why are these 3 hanging on?
I think the better way to look at it is "why did the newer flowers drop off".
Phalaenopsis buds open lowest on the spike first, and naturally fade that way too, so the loss of lower flowers is to be expected. The loss of flowers closer to the end is a likely indication that something changed in their environment.
Has the plant been in your conditions throughout, or did you acquire it partially opened?
I agree with Ray. While I sometimes have one or two hang on longer than the rest, they would usually be the end ones. If they are in the middle it seems to suggest something triggered the drop of the others.