Question
Hello
I have owned phalaenopsis for a couple years now. The plant is ready to bloom and has aboput 3 buds. One of the buds turned yellow over the weekend. DO we know what could be the probable cause? What can I do to save the other buds from doing the same?  

Answer
This may be a normal consequence of first flowering.  Plants will try to mature more buds than they can support and bud abortion is the way they shed the excess buds.  One or both of the other two buds may open normally.  The plant may simply not be strong enough to support three flowers.

Since you didn't indicate that it had flowered before, I'm assuming that it hasn't flowered for a while now.

Another, related, possibility is that the plant may have lost sufficient roots to weaken its ability to support flowering.  I would wait and see what happens to the other two buds.  They may open normally.  If the plant otherwise seems to be in good health, I would repot it after it is done flowering.  If the remaining buds also abort, I would take it out of its pot and examine the roots to see if there are any mushy, dead roots. If so, remove them and repot the plant in fresh mix.

Look at it this way.  A plant has just so much energy to distribute to new growth and to flowering.  If it puts too much energy into flowering, new growth receives a setback and the plant goes into decline.  Aborting buds, is a way for the plant to conserve its energy to build new leaves and increase its overall strength.  In this latter instance, future blooming will have more buds and better flowers.  I will emphasize that this is normal for a healthy plant.  When it happens to a plant that has lost some of its root mass due to rot, it is a cry for help.