Preheat the oven to 375°F. Line a baking sheet with parchment paper.
In a large mixing bowl, combine the chopped spinach, feta cheese, ricotta cheese, Parmesan cheese, flour, green onions, garlic, oregano, salt, pepper, and egg. Mix until well combined.
Lay one sheet of phyllo dough on a clean surface and brush lightly with olive oil. Place another sheet on top and brush with more olive oil. Repeat this process until you have 4 layers.
Cut the layered phyllo dough into squares, about 4x4 inches. Place a spoonful of the spinach and cheese mixture in the center of each square. Fold the corners of the phyllo over the filling to create a parcel and pinch to seal.
Place the filled parcels on the prepared baking sheet. Brush the tops with olive oil.
Bake in the preheated oven for 20-25 minutes, or until golden brown and crispy.
Serve warm as an appetizer or snack.