Combine the first six pho ingredients in a pot and bring to a boil over high heat. Turn the heat to low and let the mixture steep, undisturbed, for 30 minutes.
Strain the beef stock mixture into a heatproof bowl, and then pour the strained stock back into the pot. Set the pot over medium heat and mix in the soy sauce and fish sauce, if using.
Season the stock with salt and freshly ground black pepper to taste.
Fill a second pot with water, set over medium-high heat, and bring to a boil. Add the rice noodles and cook until tender, about 45 seconds. Drain the noodles and then divide them among 4 large Asian-style soup bowls. Add the sliced beef to the flavoured beef stock, stir once, and cook 2 to 3 minutes, or until the meat is still rare in the middle. (If you like your meat cooked more, simply let it sit in the stock a few minutes longer.) Ladle the stock and meat over the noodles.
Serve the pho with the garnishes, allowing diners to flavour theirs as they like with lime, green onion, herbs, and hot chili.