Preheat your oven to 375°F (190°C).
Thaw the frozen spinach completely and place it in a clean kitchen towel, squeezing forcefully to remove every drop of excess moisture.
In a large mixing bowl, whisk together the liquid egg whites and Greek yogurt until smooth.
Stir in the crumbled feta cheese, sliced scallions, chopped dill, minced garlic, sea salt, and black pepper.
Add the very dry spinach to the egg mixture and stir until the greens are evenly distributed.
Lightly brush a small oven-safe baking dish with a portion of the olive oil.
Lay one sheet of phyllo dough into the dish, folding the edges to fit, and brush very lightly with olive oil.
Place the second sheet of phyllo on top and brush again with the remaining oil.
Pour the spinach and egg mixture into the center of the phyllo-lined dish.
Fold any overhanging edges of the phyllo dough back over the top of the filling to create a rustic border.
Bake for 30 to 35 minutes until the filling is firm and set, and the phyllo crust is deeply golden and crisp.