Wring the spinach as dry as humanly possible. Transfer spinach to a large bowl and break up into small pieces.
Heat the oil in a large skillet over medium and add the leek and onion, cook until translucent, about 5-8 minutes. Add scallions and garlic and cook until tender, 2 minutes more and season with salt and pepper. Scrape into a bowl with spinach.
Whisk together the egg, egg yolk, 1 tsp salt, and ½ tsp black pepper in a small bowl and add to the spinach mixture. Add feta, Parmesan, mozzarella basil, dill, and lemon zest and mix until evenly combined. Preheat oven to 350°
Lightly brush the bottom and sides of 9 inch springform pan with butter. Working quickly, brush butter on 1 side of 1 phyllo sheet. Transfer phyllo, butter side up to the prepared pan, covering bottom of pan. Gently press and tuck sides of sheet into bottom edges of pan. Fold and ripple phyllo as needed to cover the bottom of pan. Repeat with 2 more phyllo sheets.
Working quickly, brush butter on 1 side of another phyllo sheet. Transfer to pan, arranging butter side up and slightly off-center so long side of dough comes up and over side of pan, leaving a 2" overhang. Rotate pan slightly and repeat with another sheet so overhang covers another section of pan. Continue with remaining 7 sheets, rotating pan so there is overhang around the entire pan.
Scrape spinach mixture into pan, pressing down firmly and smoothing top. Gently fold phyllo overhang over spinach mixture and continue to press until phyllo goes just below rim of pan. Don’t worry if phyllo breaks or tears; gather any broken pieces and arrange where spinach peeks through. You want the phyllo to look draped over the top with lots of waves and folds.
Bake pie until phyllo is golden brown and slightly darker around the edges, 50–65 minutes. Let cool in pan 1 hour before removing the ring. Slice and serve warm or at room temperature.