Place the oxtails in a large stockpot and add the water.
Bring the water to a full boil, then reduce heat and bring water to a simmer.
Scrape any scum off the top of the water and discard.
Cut the onion in half and peel off the outer portion.
Place on a baking sheet along with the ginger and broil in the over about 20 minutes, making sure not to blacken it.
Turn over halfway through.
Allow to cool.
Place the star anise, cloves, cinnamon, and fennel seeds in a piece of cheesecloth and tie it shut with twine.
Add the spice pack, onion halves, ginger, bay leaves, salt, and fish sauce to the broth.
Allow the broth to simmer at least 5-6 hours (to your taste) uncovered.
Remove the spice pack, onions, ginger, and bay leaves and discard.
Remove the oxtails and set them aside.
When cool enough to handle, remove the meat and trim of any remaining fat.
Set the meat aside and return the bones to the broth.
Allow the broth to simmer another hour or two until you achieve the desired taste then remove the bones.
You may adjust the salt, but you don't want it too salty.
Soak the rice noodles in COLD water 15-20 minutes, while starting a large pot of water boiling.
While the noodles are soaking, place the cilantro, basil leaves, mint leaves, sliced onions, sliced scallions, and bean sprouts on a serving platter.
After the noodles have soaked, place them in the boiling water and allow to cook until tender, but don't let them get mushy.
It should only take a couple minutes.
Rinse the noodles in cold water if not serving immediately.
When ready to eat (you can do this earlier, like when you're boiling the water for the noodles) return the broth to a rolling boil.
Place the noodles in a serving bowl and arrange the sliced meat (leftover oxtail meat if desired) over them.
Ladle the boiling broth over the noodles and beef, making sure to cover the meat.
Serve and allow each person to place the desired amount of garnish from the platter, hoisin sauce, and sriracha in their own bowl to taste.