You should post your questions about orchids in the Orchids Forum. It will get better noticed there.
Your Phalaenopsis is not rotting, it is wilted. That is the leaves are wilted because the root system isn't large enough or healthy enough to be able to absorb enough water to keep the leaves firm and growing horizontal.
You should as a beginner repot a Phalaenopsis every 2 years. Not because it's roots escape the pot! That is exactly what should happen as it is nearly impossible to keep healthy roots IN a pot. In nature they can wander between 3-5 meters!! After all, we grow orchids for the beautiful flowers, not to keep them neat and tidy.
By repotting into too large of a pot, that causes problems. Orchid pots should ALWAYS have drainage holes.
Plus as a beginner, sphagnum moss is a very difficult media to grow with. Why? It is easy too repot too tightly which is bad! It is easy to pot to loosely which is also bad! It is not that it won't work, it is just very tricky for a beginner to learn how to use it properly.
Here is an image of my media.
I use it for every kind of orchid that I grow. Paphiopedilums, phragmipediums, Oncidiums, Cattleya etc. it is a blend of medium grade fir bark, seedling grade bark, charcoal, perlite and aliflor. This would be much easier then moss.
For all orchid mixes and supplies, I recommend the Green Barn Orchid Supplies in Delray Beach Florida. They also sell a pre-mixed media for Phalaenopsis.
I would repot it into such a media and keep it shaded for 4-6 weeks. Within that time frame new roots will develop, take up water and plump up those leaves!!
