I can't recommend Physan 20 because I have never used it. It appears that you have Botritis fungus on the flowers. It is most common on Phals in cool damp conditions with insufficient air movement. I have gotten it in the past when my greenhouse is closed for several days. I use something called RD-20 which is a bactericide, fungicide, viriside. It is much cheaper than Physan-20, about $10.00 per qt. It is commonly used as a disinfectant to get rid of the bacteria before it becomes a problem but the drawback is that it rids the good bacteria also and that is not good. I have used it on the infected Phal flowers alone and not on the plant at one tsp. per gallon and it halted the spotting. I obtain it at
the source on the link.
http://www.tropicalplantproducts.com/