Phal Orchid leaves with patchy green and yellow areas

[Ray]

Originally Posted by sweta

Regarding the pH, I've been reading up online that for nutrients to be absorbed properly phals need slighly acidic medium like 6.5 pH. Wont it make any difference if the water content is alkaline? I dont get a great bloom show thats why wanted to see if this would change anything

If the water is high in alkalinity - which is not the same as having a pH above 7 - it will eventually shift the rhizosphere pH upward.

As far as pH affecting nutrient availability or the ability of the plant to take it up, that is only true if the pH is toward the extreme ends of the scale. Please read this and this.

Besides, microbes and the plant, itself, affect the pH far more than does the solutions applied. Prove it to yourself by doing a simple pour-through test, described in one of those articles.

@es and @ray should I treat my orchids with cal-mag just for few weeks to overcome the deficiency?

Yellowing - assuming it really is a nutrient deficiency - is caused by a lack of nitrogen and magnesium, not calcium. If you simply go to a more appropriate feeding regimen, it ought to resolve it going forward. The affected leaves may not recover.