My phaius orchids new growth keep developing rot.
 

I bought a phaius orchid a few months back and recently I moved it into a slightly large pot as it was root bound. Just before I repotted it I noticed some of the new growths starting to come out of the pseudo bulb had blackened and after I repotted it more growths have blackened as well as a bit of the pseudo bulb itself. What should I do? Its seems to start as a blue grey spot and spread from there. Also Ive only watered it when the substrates gone dry.

First, Welcome!

Others on the Board grow Phaius more than I do ( I just have two)... but one thing jumps out at me, water... I wonder if it is reacting to lack of water... I keep this one quite wet. Unlike the epiphytic orchids like Phalaenopsis and Cattleya that need to dry out, this one is mostly terrestrial, and shouldn't get dry.

The watering is what I'm not sure about as I've for the most part always kept it moist and watered it as soon as it began to feel dry

The only advice I have gotten was not to get water on the leaves or new growths (my Phaius is indoors in a window, not much air movement). I have been watering from below and carefully at the soil line.

When I see new growths rot like this, I always wonder if it might be Calcium deficiency. Calcium tends to strengthen the cell walls but it must be given to the plant before and during new growth.
Here is a pair of videos explaining the role:

Frontiers | Calcium—Nutrient and Messenger | Plant Science

Role of Calcium in Plant Culture | PRO-MIX Greenhouse Growing

Good luck!

The few I've seen growing wild are always wet. They never get aywhere near dry.

How would you recommend adding calcium? As some of it has now spread to the pseudobulb itself and the roots were fine.

Cali Magic, crushed oyster shell, (if outside, powdered milk--the milk will sour and smell), lime, etc. If you have a hardware store nearby, they would probably be able to recommend something. As it is spreading, you might need to look into a systemic fungicide.

Good luck!