Just to be on the safe side, you should always check for mites on the underside of leaves every time you see some unexpected behavior of an orchid. I have had all sorts of leaf loss problems with Phals, and in the end it was not mites, but one needs to always be vigilant for them. I some times think that any upset can cause leaf loss, well that is the only conclusion I can come to, as I have still not found the cause. So, I have been careful to not have too much light, a cause of leaf loss, not to allow water on the leaves that is too cold, sunken spots on leaves, and have started the use of a systemic fungicide recently that may be helping.
Checking For Mites