Preheat oven to 375°F. Spray a 12-cup mini-muffin pan with nonstick spray.

Place 1 phyllo sheet on a work surface. Cover the remaining sheets of phyllo with plastic wrap to keep them from drying out as you work. Lightly spray the phyllo sheet with nonstick spray; top with a second phyllo sheet and lightly spray with nonstick spray. Repeat with the remaining phyllo sheet to form a stack. With a sharp knife, cut the layered sheets lengthwise into four rectangles, then crosswise into three rectangles, making a total of 12 rectangles.

Place a rectangle into each muffin cup pressing gently to form a shell. Sprinkle each shell evenly with the Parmesan cheese. Bake 3 minutes. Remove from the oven (leave the oven on). Place one tomato slice in each tartlet and sprinkle evenly with the mozzarella. Bake until cheese is melted and the phyllo is crisp and lightly browned, about 3 minutes. Top each tartlet with a basil leaf and serve at once.