Heat olive oil in a Dutch oven over medium-high heat until hot. Add green onions and garlic; sauté 3 minutes or until tender. Add spinach and water; cover and cook 8 minutes or until spinach wilts. Cool spinach completely in a colander set over a bowl. Return cooled spinach to pan. Add cheeses, tomatoes, oregano, 1/2 teaspoon salt, and pepper, stirring well to combine.
Trim phyllo sheets to 13" x 9", if necessary. Layer 8 sheets of phyllo in a lightly greased 13" x 9" baking dish, using half of melted butter to brush between sheets. (Keep remaining phyllo covered with a damp cloth.) Bake at 400° on lowest oven rack for 6 minutes or until lightly browned; set aside.
Melt 1 tablespoon butter in a small saucepan over medium heat. Stir in flour; cook 1 minute. Gradually whisk in milk. Cook over medium heat 2 minutes, whisking constantly. Whisk in cream cheese and remaining 1/4 teaspoon salt.
Spread spinach filling over baked phyllo crust; drizzle with white sauce.
Layer remaining phyllo sheets over filling using remaining half of melted butter to brush between sheets. Using a sharp knife, score top layer of phyllo into 8 portions. Bake at 400° on middle oven rack 30 minutes or until pastry is golden. Serve hot.