so I had a similar but much less severe spotting developing on one of my philos and I treated with a product called fertilome triple action plus. it never developed spots after treating it and the new leaves haven't developed spotting!
https://www.amazon.com/Voluntary-Purchasing-Group-Concentrate-Triple/dp/B00D8NQ26C/ref=sr_1_2?dchild=1&keywords=fertilome+triple+action+plus&qid=1633325724&sr=8-2 This is the product I used but I bought it locally in like a spray bottle size
You are correct. This is what I was recommended to use by my local garden center when dealing with mealybug infestation:
https://www.amazon.com/Voluntary-Purchasing-Group-Concentrate-Triple/dp/B00D8NQ26C
It it’s a triple action, fungicide, matricide, insecticide.