Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Mix until smooth and well blended.
Stir in the grated Parmesan cheese and shredded mozzarella cheese until evenly incorporated.
Add the chopped artichoke hearts, chopped spinach, minced garlic, onion powder, salt, black pepper, and red pepper flakes (if using). Mix until all ingredients are well combined.
Transfer the mixture to a baking dish and spread it evenly.
Bake in the preheated oven for 25-30 minutes, or until the dip is hot and bubbly and the top is lightly golden.
Remove from the oven and let it cool for a few minutes before serving.