Spider Mites Or Sun Burn

If the photo were taken just a little closer an identification might be more accurate, however:
1. look on the underside of the leaf and see if there are any webs. They could also be found where the stem meets the leaf and where the stem meets the stalk. If webs are present then you have spider webs and it must be treated with insecticidal soap (available at garden centers and home improvement stores) every seven to ten days until it clears up. You can also place a piece of white paper beneath the leaf. If there any very, very small yellow or red dots crawling around after the leaf is tapped several times, you have spider mites. 2. The foliage also could be from sunburn. Has the plant come from a shady location to a bright light or grown indoors and placed outdoors in bright light? Philodendron xanadu requires filtered indoor light or partial shade outdoors. 3. It could also be from a buildup of unsoluable fertilizer salts in the soil. Take the plant outside (in a shade location) and water the plant five or six times filling the pot up to the top each time and allowing the water to completely drain. This action will “flush” the bad salts from the soil. Afterwards, you might want to think about repotting the plant with good potting soil.