Hi,
I have a philodendron for around a year. Everything was fine but lately on a new leaf a saw a white spots and some discoloration. I have checed all the plant but i didn;t seen any pests. The soil contains coco chips, perlite, compost. I water it when needed (about once a week with filtred water). It's near south facing window but not in direct sunlight. In summer I fertilzed it onec a month with biohumus.
Please help.

That looks to me like thrip damage. Just because you don't see them doesn't mean they weren't there or aren't still there. I would treat it with insecticide if it were mine