I have Phals with the exact same symptoms. New leaves are fine, and after a few months they start to look like that. Working at a place with a plant diagnostics lab, I had the luxury of being able to give a colleague samples from 6 different Phals, and he tested them for 6 different viruses common on orchids. All the tests came back negative... He did not do further tests for bacterial/fungal disease because it was too expensive to do pro-bono for me. (involves sequencing a segment of the pathogen DNA and blasting it against a database).
The official assessment of the lab is insect damage. I did have a mealybug problem at the same time, but not on the scale that would cause such symptoms on the plants.
After more searching on the web, I can across a french blog post of someone dealing with the same thing.
Ravageurs ou Maladies - Les Orchidees de Sophie.com (you can put it through google translate).
A few ideas from the comment of that post: It can be due to mites, but not the red ones so won't show up if you wipe a leaf with cotton. They suggest treating with a miticide or rubbing alcohol with cinammon steeped in it (do not use on roots). Other possibility was something fungal that people are calling 'microfungus', and recommended a systemic fungicide such Funginex.
Not having access to systemic fungicides (Netherlands banned the sale of many chemicals a few years ago), I'm watching and waiting to see if the new leaves stay symptom free, after having treated the plants with insecticide (for the mealies) and acaricide.
If you have just one plant affected (that last photo is normal leaf mottling), I would trash it. I'm hesitant to do that because I have many Phals affected, and Phals represent the bulk of my collection. I've trashed the really badly affected plants for now.
Phalaenopsis with disease
Linear Mode
