Preheat the oven to 375°F.
In a non-stick pan, drizzle olive oil and sauté finely chopped onion and minced garlic until softened and fragrant.
Add the fresh spinach to the pan and gently sauté until just wilted. Season with a pinch of salt and pepper, then remove from heat.
In a mixing bowl, lightly beat the eggs and egg whites. Stir in the crumbled feta cheese.
Combine the sautéed spinach mixture with the egg and feta mix, ensuring everything is evenly distributed.
Lay one sheet of phyllo dough on a lightly greased baking tray, brush lightly with a bit more olive oil, and layer the second sheet on top.
Spread the spinach, egg, and feta mixture evenly over the phyllo sheets, leaving a small border around the edges.
Fold the edges of the phyllo over the filling to form a neat pie, and make a few slits on top to allow steam to escape.
Bake in the preheated oven for 20-25 minutes or until the phyllo is golden and crispy.
Remove from the oven, slice, and serve warm.