Question
My phal's new flower spike started growing, looked fine, and then started growing in red almost overnight. There is about a centimeter of healthy green stem, and then a centimeter more of reddish growth of stem. what is causing this red growth? what do i do?

i water once weekly and they all have partial filter light. the other orchids i have are doing fine.

Answer
Sarah, thanks for your question. Has this plant previously flowered?  The reason I asked is that phals trying to flower the first time will sometimes abort the new flower spike as they don't have the strength to produce and open buds. In this case, the reddish coloration is the first stage in flower spike die back. On the other hand, if  this phal has a pink flower, this pigment build up in the flower spike is in anticipation of flowering and will migrate out of the flower spike and into the flower when opening.  These plant pigment are water soluble and readily migrate from one part of the plant to another, but, usually concentrating in the flower parts.

Based upon your description, these would seem to be the two most likely causes and are natural.