Dice the onions, mushrooms, and peppers.
Heat a large skillet or dutch oven (5qt or larger) to medium heat and add italian sausage, breaking it into small crumbles as it cooks.
Once the meat is browned, drain any excess fat.
Add the garlic, onion, peppers, and mushrooms to the pan and cook for 3-5 minutes, until soft.
Add the salt, pepper, red pepper flakes, and Italian seasoning. Stir to combine.
Add the broth, tomato sauce, milk, and pasta.
Mix everything together and bring to a simmer.
Lower the heat to medium low and cover for 8 minutes, stirring occasionally to make sure nothing is sticking to the bottom of the pan.
Uncover the pan and continue cooking for another 5-7 minutes or until the pasta is al dente, stirring occasionally.
Add the cream cheese and parmesan cheese and stir until incorporated.