Preheat your oven to 375°F (190°C).
In a medium bowl, mix the cream cheese, sour cream, and mayonnaise until smooth and creamy.
Add the minced garlic, salt, black pepper, and crushed red pepper flakes (if using). Stir well to combine.
Fold in the chopped spinach, shredded mozzarella, and Parmesan cheese. Mix until everything is evenly combined.
Spread the mixture evenly into a small oven-safe baking dish.
Bake uncovered for 25 to 30 minutes, or until hot and bubbly on top. The edges should turn slightly golden and the cheese should melt beautifully.
Remove from the oven and let it rest for 5 minutes before serving.