Turn on the Instant Pot and set to the 'Sauté' function. When hot, add the onion and ginger. Sauté for about 5 minutes until charred.
Add the beef bones to the pot and sauté for an additional 3-4 minutes.
Add the star anise, cinnamon stick, coriander seeds, fish sauce, and water to the Instant Pot. Stir to combine.
Close the lid securely, set the valve to sealing, and cook on 'Manual' or 'Pressure Cook' for 25 minutes.
Once cooking is complete, allow for a natural pressure release for about 10 minutes, then switch the valve to venting to release any remaining pressure.
Carefully remove the beef bones and strain the broth through a fine mesh sieve into a large bowl to remove spices and solids. Return the clear broth to the Instant Pot.
Set the Instant Pot to 'Sauté' again. Add the sliced brisket to the pot and cook for 5 minutes until just cooked through.
Meanwhile, cook the rice noodles according to package instructions and drain.
To serve, place a portion of the noodles into bowls, ladle the hot broth with brisket over the noodles, and garnish with fresh basil, cilantro, lime wedges, and optional sauces.