Heat the oven to 375°F and place a lightly greased 1.5–2 quart baking dish on the center rack to warm while you prep.
In a medium saucepan over low heat, stir the cream cheese with the roasted garlic Alfredo sauce until completely smooth and glossy, 3–5 minutes. Remove from heat.
Whisk in the sour cream, Parmesan, 1 1/4 cups of the mozzarella, lemon zest, crushed red pepper flakes, and black pepper to taste.
Squeeze the thawed spinach in a clean kitchen towel until no liquid drips. Pat the drained artichokes dry with paper towels and chop. Fold both into the warm cheese base until evenly distributed.
Carefully pull the hot baking dish from the oven, scrape in the dip, and smooth the surface. Sprinkle the remaining 1/2 cup mozzarella over the top.
Bake until the edges are bubbling and the top is melty, 18–22 minutes. For extra color, broil 1–2 minutes. Let rest 5 minutes before serving so it thickens slightly.
Serve warm with tortilla chips, crackers, toasted baguette, or pita wedges.