Place the flank steak in the freezer for 15 minutes to firm up, then slice against the grain into paper-thin strips.
In a medium pot, toast the star anise and cinnamon stick over medium heat for 2 minutes until fragrant.
Add the sliced ginger and beef bone broth to the pot, bringing it to a gentle simmer for 10 minutes to infuse the flavors.
While the broth simmers, cook the rice noodles in a separate pot of boiling water according to package directions, then drain and set aside.
Stir the fish sauce into the broth and remove the whole spices (star anise and cinnamon).
Place the cooked noodles in a large bowl and arrange the raw, thinly sliced beef on top of the noodles.
Pour the boiling hot broth directly over the beef slices; the heat from the broth will cook the thin meat instantly.
Garnish the bowl with bean sprouts, scallions, cilantro, and Thai basil.
Serve immediately with a lime wedge and a drizzle of sriracha for a clean, spicy finish.