Combine cream cheese, sour cream, mozzarella, parmesan cheese and garlic in a large mixing bowl with a hand mixer and stir until everything is combined. Stir in artichoke hearts and lastly chopped spinach. Transfer the mixture to the bowl of your slow cooker, that has been misted on the inside beforehand with cooking spray.
Slow cook the spinach and artichoke dip on low for 3-4 hours or on high or low for 2 hours. You'll know the dip is done cooking when it's deliciously melted and spreads perfectly on a pita chip, bagel chip or cracker - YUM! Give the dip a good stir and season with extra salt and pepper if needed.
I am usually serving this to a group of people that help themselves, so a 2-3 quart crock pot is perfect, but you could also transfer the dip to a dish to pass at a table.