I have seem something like that before, but I'm afraid to say it was on a Phal which a few months later died of a spreading hard dry black necrosis (which took several months to spread arround the crown and kill it).
I have no idea if the white spotting was at all related to what killed it and there is a good chance it's completely unrelated.
Unfortuantely I also don't know what was the cause of either the spotting or the thing which killed my orchid
Just wiping it off is not going to treat the cause of it. Have you changed your culture conditions lately? (humidity, temperature, light, watering frequency...)
__________________ Camille
Completely orchid obsessed and loving every minute of it....