Normally I would never suggest that an orchid beginner uses sphagnum moss as a media. It is a media that beginners struggle with because of watering. Is it dry enough or should I wait? Is it still too damp? Plus the moss works much better with New Zealand Long fibred moss. Many people don't use the correct moss.
Additionally New growers can leave it too loose or pack it too tight. If you repotted using moss and the plant developed root rot shortly after, you most likely packed it too tightly.
Phalaenopsis like a bright location without any sunshine. They need to be watered well and then approach dryness before they are watered again.
Yellow leaves at the bottom are lost most often due to senility or old age. They don't last forever.
Lastly check out the forums here on "Supermarket Phalaenopsis" and others regarding their culture. I posted a thread last June I think on how I repot Phalaenopsis. Also check out the American Orchid Society website: AOS.org and look within at the top of the page pull down for their culture sheets. They are downloadable and printable pdf files. Get the one in Phalaenopsis Culture.
