It's a fungus akin to botrytis. Such fungi aren't uncommon, and probably won't effect the plant itself, just the flowers. However, when dealing with fungi I personally prefer all-out warfare. You may choose to leave the flowers (I wouldn't), but my reaction to finding this would be to spray the plant with a copper-based fungicide. Now remember, I'm the eternal pessimist and so I expect everything to go wrong - it's quite possible you'll hear from others who say to leave it alone, or to just pick off the infected flowers. Plus, I like the word fungicide.
However you deal with it on this plant, an important thing to consider is why it developed in the first place. Spores for these various fungal blights just are. By that, I mean they're everywhere. Grape fields in France, orchid greenhouses in Malaysia, and windowsills in Smyrna, Georgia. Phalaenopsis plants love high humidity but high humidity encourages fungal growth. When the humidity level is nice and high it's important that there is good air circulation. Probably the spores got onto the plant aided by the stagnant kitchen air where, aided by stagnant air, they began to sprout. You then noticed them in the greenhouse, where the air likely moves a lot better but where the fungus had already taken hold (or, Plan B, maybe your greenhouse needs better circulation?).
A lot of my plants, mostly Phals, live in a grow window that a previous owner installed in the kitchen. It has an air vent at the top but in the winter the vent allows too much cold through. I placed a couple of very small, personal fans, one on each side, to cause a gentle breeze through and across the window. If I could afford to do so, I would give a couple of these fans to every single person in the world who owns a Phalaenopsis.
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