Cook ground turkey in skillet over med-high heat. Drain, season with garlic powder and black pepper. Set aside.
Combine spinach, cream cheese, feta and chopped artichoke hearts. Set aside.
Spray the bottom and sides of the tart pan with nonstick cooking spray.
Line the tart pan with 8-10 layers Phillo dough. Do not butter each layer as you normally would when working with Phillo.
Spread half of the spinach mixture into the bottom. Follow with a layer of ground turkey.
Cover this with 6-8 layers Phillo dough.
Layer the rest of the spinach mixture and ground turkey into the pan.
Cover with another 6-8 layers Phillo dough, pressing down into the perimeter of the pan (you want to be sure to encapsulate the ingredients, and make sure the upper layers of Phillo don't flake off during baking). Any extra dried dough sticking up around the edge may be removed.
Bake at 350F for 45 minutes or until Phillo is golden.