This looks very much what I used to see on Phals in my early days of Orchid growing ca 25 years ago. The plant would grow a new healthy leaf, then these lesions would start which turned into large sunken areas and eventually killed the whole leaf. After a while the leaves would fall off in a faster rate than growing new leaves and the plant died. The reason was supposed to be micro fungus.
I quit growing Phals then for at least 15 years.
