Place the oxtail and beef bones into a large pot and cover with water. Bring to a boil for 10 minutes. Drain, rinse the meat and bones thoroughly, and wash the pot.
Halve the onions and slice the ginger lengthwise. Broil them or char them directly over a gas burner until nicely blackened.
In a dry skillet over medium heat, toast the star anise (if using), cinnamon stick, and cloves for 30–45 seconds until fragrant.
Add the cleaned oxtail, beef bones, charred onions, charred ginger, toasted spices, water, beef bouillon, kosher salt, and sugar to the Instant Pot. Do not add the fish sauce yet.
Seal the lid and cook on High Pressure for 90 minutes. Allow a natural pressure release for 15–20 minutes.
Strain the broth, discarding the bones, onions, ginger, and spices. Remove the meat from the oxtail and reserve it for serving.
Turn the Instant Pot to Sauté. Stir in the fish sauce and taste the broth. Adjust with additional fish sauce, beef bouillon, sugar, or salt if needed. The broth should taste rich and beefy with a subtle hint of warm spice.
Cook the rice noodles according to the package directions.
Divide the cooked noodles between serving bowls. Top with thinly sliced raw ribeye or sirloin and the reserved shredded oxtail meat.
Ladle the piping hot broth over the beef to cook it instantly.
Serve with green onions, sliced white onion, cilantro, bean sprouts, lime wedges, jalapeños, hoisin sauce, and sriracha.
