Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and bell peppers (both green and red). Cook, stirring occasionally, until the vegetables are softened and slightly caramelized, about 8-10 minutes.

Add the thinly sliced sirloin steak to the pot. Increase the heat to medium-high and cook, stirring frequently, until the steak is browned. Be careful not to overcrowd the pot; you may need to do this in batches to ensure the steak browns properly instead of steaming.

Pour in the beef broth and add the diced tomatoes (with their juices). Stir to combine, scraping up any browned bits from the bottom of the pot.

Stir in the Worcestershire sauce, dried thyme, and red pepper flakes if using. Season with salt and pepper to taste. Bring the soup to a simmer, then reduce the heat to low, cover, and let it simmer for at least 30 minutes, or up to an hour.

While the soup is simmering, prepare the cheese sauce. In a medium saucepan, melt the butter over medium heat. Once melted, whisk in the flour and cook for 1-2 minutes, stirring constantly, to create a roux.

Gradually whisk in the milk, about 1/2 cup at a time, ensuring each addition is fully incorporated before adding more. Continue whisking until the sauce is smooth and thickened.

Reduce the heat to low. Add the softened cream cheese and stir until it is completely melted and smooth. Then, add the shredded provolone and mozzarella cheeses, a handful at a time, stirring until each addition is melted and the sauce is creamy and smooth.

Stir in the garlic powder, onion powder, salt, and pepper to taste. Adjust the seasonings as needed to your preference.

Once the cheese sauce is ready, slowly pour it into the pot with the soup base, stirring constantly to combine.

Heat the soup through, stirring occasionally, until it is heated through. Be careful not to boil the soup after adding the cheese sauce, as this can cause the cheese to separate.

If the soup is too thick, you can add a little more beef broth to thin it out. If it’s too thin, you can simmer it uncovered for a few minutes to allow some of the liquid to evaporate.

Ladle the Philly Cheesesteak Soup into bowls. If desired, top with extra shredded provolone or mozzarella cheese and chopped fresh parsley. Serve immediately with crusty rolls for dipping.