Preheat your oven to 350°F (175°C).
Thoroughly drain the thawed spinach by squeezing it in a clean kitchen towel to remove excess moisture.
In a large mixing bowl, combine the softened cream cheese and mayonnaise until smooth.
Add the minced garlic, red pepper flakes, salt, and black pepper to the cream cheese mixture.
Stir in the Parmesan cheese and 3/4 cup of the mozzarella cheese.
Fold in the drained spinach and chopped artichoke hearts until well combined.
Transfer the mixture to a 9x13 inch baking dish.
Sprinkle the remaining mozzarella cheese on top.
Bake for 25-30 minutes until bubbly and lightly browned on top.
Let rest for 5-10 minutes before serving.