My understanding is sunburn happens in the center of leaves and fertilizer burn happens on the edges. So yes, sunburn.
Phalaenopsis hate sun and overwatering. Move the plant to a shadier area, water when the medium is dry and stop with the fertilzer. My Phals are fertilized just a few times a year and bloom amazingly. I like clear plastic pots because I can see the moisture and if I see moisture, I don't water.
