Phal Orchid leaves with patchy green and yellow areas

[sweta]

Hi Orchid Pals,

I have had this grocery store bought phal for about 3 years now. 1st year it rebloomed but after that had scale infection so it went though a setback for a period of time but its been doing good past few months with new leaves and healthy roots. Now I see that now the leaves have suddenly turned patchy and slowly dying off. There are 2 to 3 more of my phals that are showing similar signs that have been close to this one. Is it bacterial or fungal disease and what treatment can I give it so its healed from the disease? I'm attaching pictures. Home temperatures are arounr 70F watered weekly, fertilized biweekly.