Question
My Phalenopsis orchid flowered beautifully last in July 2008.  This year they have all put up flower spikes but the leaves on 2 have gone yellowish, and droped off - the spike still there though.  They are in their individual pots in a larger bowl which has moss and ivy growing in it.  A light conservatory but cold at night.  

Answer
Doreen, there are several issues here.  First, and foremost, is that you need to repot your phalaenopsis into a plastic pot with lots of drainage holes in it using a standard orchid potting mix.  When you unpot your plant prior to repotting, rinse off the roots and remove any that are mushy or stringy-- these are dead.  Do not permit the repotted plant to sit in water.  If you choose to have the potted plant rest in another container, it should be such that you should remove the potted phalaenopsis from the other container while watering and let it drain completely before replacing it in the container  It is generally recommende that phalaenopsis be repotted in a standard orchid potting mix after each flowering.  Phalaenopsis, unlike other orchid plants, need an open potting mix to permit rapid drainage and abundant air flow to the roots.  A standard orchid potting mix is designed to do that.

The second issue is temperature.  Phalaenopsis need to be grown at temperatures that range not below 65 degrees F.  They are tropical in nature and do not do well at temperatures below that. Cool night temperatures plus a degraded potting mix and excesssive moisture is a recipe for disaster so evaluate your growing conditions based upon this advice and make any changes that seemed warranted.