Parboil the oxtail – Fill a large pot with water and add in the oxtails, ensuring there is enough water to fully cover the oxtails. Bring the water to a boil and let simmer for about 5 minutes until the water turns cloudy with debris rising to the surface. Drain the water, and remove the oxtail pieces from the pot.
Toast the spices and – In a skillet, toast the cinnamon stick, coriander, cloves, and star anise until fragrant, about 1-2 minutes.
Char the aromatics – Cut the ginger and yellow onion so that it has a flat surface area and roast it in a skillet or on an open flame on the stove.
Make the stock – In a large pot, add about 4 cups of water and the oxtails, along with the toasted spices and charred aromatics. Bring to a simmer and let simmer for at least 4 hours.
Prepare the noodles and garnishes – When the stock is about to be ready, cut the garnishes in preparation for putting together the noodle bowl. Slice the chili peppers, limes, and scallions. And cook the pho noodles according to the package instructions.
Adjust the stock – Once the stock has reached its cooking time, add the fish sauce and sugar and stir thoroughly.
Serve and enjoy – In a large bowl, add the noodles, add the hot broth, garnish with cilantro, green onions, chili, and lime, and enjoy!