Preheat the oven to 325F.
Wash spinach leaves, drain off excess water. Dry on the kitchen towel and chop roughly.
In a pan, melt butter, add garlic powder, add spinach leaves and cook till all the water from the leaves dries.
Transfer the leaves to a bowl, once it cools down, add and mix feta crumbles and grated mozzarella cheese.
Open the Phyllo Sheet pack, take out one roll and keep the sheets covered in a damp kitchen towel.
Put one sheet on the baking dish, brush some melted butter, put another sheet on top of it. Likewise repeat the steps with 4-5 sheets.
Spread the filling evenly on the pastry layer.
Cover the filling with one phyllo sheet, brush the top of the sheet with butter and put another sheet on top of it. Likewise repeat the step for the rest 4-5 sheets.
Tuckin the corners of the sheets on the side, to seal the edges.
Brush the top layer with butter or egg wash and bake it in the preheated oven for 50-60 minutes or till the top layer is flaky and brown in color.
Once done, take out of the oven and serve hot.