Boil pasta in salted water until al dente. Save 1 cup of pasta water before draining.
Heat olive oil in a large skillet over medium heat. Add sausage and cook until browned.
Add sliced fennel and garlic to the skillet. Cook until fennel softens.
Stir in Calabrian chili paste and cook for 1 minute.
Pour in heavy cream and simmer until slightly thickened.
Add cooked pasta to the skillet and toss to coat with the sauce.
Stir in Parmesan cheese and adjust consistency with reserved pasta water if needed.
Season with salt and pepper to taste.
Serve hot, garnished with fresh basil leaves.