In a large bowl, mix together the spinach, feta, sour cream, garlic powder, onion powder, dried oregano, and white pepper. Stir until all is thoroughly combined. Taste mixture and add salt, if needed.
Place all phyllo shells on a baking sheet and fill each with 1 tablespoon of the spinach/feta mixture. Baked in preheated oven for 12-15 minutes, until mixture is heated throughout and shells are nice and toasty. Serve immediately.