Heat the pot over medium-high heat. Add the remaining 2 tablespoons butter and stir until melted. Add garlic and cook, stirring, until fragrant, about 1 minute. Add flour and cook, stirring, for 30 seconds. Gradually whisk in milk. Bring to a boil, whisking constantly. Continue cooking and whisking until the mixture thickens, about 5 minutes. Remove from heat. Stir in cream cheese, mozzarella and salt.