Question
I received a healthy, big phal orchid as a gift about two months ago.  It had two stalks with flowers and buds, about 18" tall.  I decided to keep it in my office,thinking the temperature would be more stable, and because I have a little 6 gallon aquarium with an open top, which I figured would help with humidity.  The orchid is next to the aquarium, with the blooms hanging over the water.    
Soon, however, the buds fell off.   The rest of the plant seems healthy.    
Now, I have yellow leaves falling off.  I've already lost two and have another on the way out.   This leaf also has black spots and a black rim.  I thought this was possibly from too much light from the aquarium (it's a planted aquarium with a grow light).  Now I'm worrying it's fungus.  I've only needed to water the plant once in two months, which I did in the early morning on a warm day.  The substrate is still moist.   

Any suggestions on how I can get it healthy again?  The flowers are now starting to wilt and fall off, and I am planning on just cutting back the stalk and not trying for a rebloom.
Thanks!
Meri

Answer
I do have a suggestion.  From your description, there is a good chance that your plant has the start of root rot.  I recommend that you purchase a bag of orchid potting mix, then unpot your plant, wash all of the old potting mix from the roots and remove any "mushy" roots.  These roots are rotted and no longer serve any useful purpose.  By doing this you will be able to asses the overall condition of your roots and how many good, healthy firm roots you have to support future growth.  Ideally,  phals should be repotted annually after they finish flowering.  Healthy roots are the key to a healthy plant.  After repotting in fresh orchid potting mix, you may still lose those leaves that are now yellowing or look unhealthy (you may cut them off if you choose).  With a fresh orchid potting mix, you should have a good draining mix such that you can water at least weekly.  If you have an east facing window in your office, the plant should do well with some morning sun.  They need temperatures  65-80 degrees as ideal but can tolerate temperatures a little above or below that. After repotting, you should be able to see new growth on your plant in 4-8 weeks.