Sauté Aromatics. Set the Instant Pot to sauté mode and heat olive oil. Add diced onions, bell peppers, and garlic, then sauté until softened.
Brown Sausage. Add Italian sausage to the pot and cook until browned, breaking it apart with a spoon as it cooks.
Add Ingredients. Stir in crushed tomatoes, chicken broth, Italian seasoning, and pizza sauce. Season with salt and pepper to taste.
Pressure Cook. Secure the lid and set the Instant Pot to manual high pressure for 5 minutes. Once cooked, allow for a natural pressure release for 10 minutes before quick releasing any remaining pressure.
Add Toppings. Stir in sliced pepperoni and shredded mozzarella cheese until melted and gooey.
Serve. Ladle the soup into bowls and garnish with grated Parmesan cheese and fresh basil leaves. Serve hot and enjoy!