In a large pot of boiling salted water, cook the fettuccine according to package instructions until al dente. Reserve 1/2 cup of pasta water, then drain and set aside.
In a large skillet over medium heat, add olive oil and sauté minced garlic until fragrant, about 1 minute.
Reduce heat to low and add cream cheese, stirring until melted and creamy. Mix in the sour cream, mozzarella cheese, and Parmesan cheese until the mixture is smooth.
Stir in the thawed spinach and chopped artichoke hearts. If using, add red pepper flakes, and season with salt and pepper to taste. Let the mixture simmer for 5 minutes, stirring occasionally.
Add the cooked fettuccine to the skillet, tossing everything together. If the mixture is too thick, gradually add reserved pasta water to reach desired consistency.
Once well combined and heated through, remove from heat.
Garnish with fresh parsley before serving for a burst of color and flavor.