Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Mix until smooth and well-combined.
Add the thawed and drained spinach, chopped artichoke hearts, mozzarella cheese, Parmesan cheese, minced garlic, salt, black pepper, and red pepper flakes (if using) to the bowl. Stir until all the ingredients are evenly mixed.
Transfer the mixture to a 9-inch baking dish and spread it out evenly.
Bake in the preheated oven for 20 to 25 minutes, or until the dip is hot and bubbly and the top is slightly golden.
Remove from the oven and let it cool for a few minutes before serving. Enjoy with your choice of chips, crackers, or sliced bread.
Optional: Prepare the dip ahead of time and refrigerate it before baking. Just add a few extra minutes to the cooking time if baking it straight from the fridge.
Feel free to customize the dip by adding other ingredients like chopped green onions, bell peppers, or even cooked bacon for extra flavor.