Thaw the frozen chopped spinach and drain it thoroughly to remove excess moisture.
In a mixing bowl, combine the softened cream cheese, sour cream, mayonnaise, mozzarella cheese, and Parmesan cheese. Mix well until creamy and fully combined.
Stir in the chopped spinach, drained artichoke hearts, minced garlic, salt, black pepper, and red pepper flakes, if using. Combine all the ingredients until evenly mixed.
Transfer the mixture to the crockpot. Spread it out evenly and cover with the lid.
Set the crockpot to low heat and cook for 2 hours, stirring occasionally.
After 2 hours, check for consistency. If it is heated through and creamy, it's ready to serve. For a thicker dip, you may continue cooking for an additional 30 minutes on low.
Serve warm with tortilla chips, pita bread, or sliced veggies. Enjoy!