Bring a large stockpot with water to boil over high heat. When it comes to a rolling boil, add the beef bones and boil vigourously for 10 minutes.
In the meantime, heat a frying pan on medium-low heat. Add the Vietnamese Pho Spices and toast until fragrant, about 2-3 minutes. Dump the spices to the empty Crock Pot or slow cooker immediately. Return frying pan to medium-high heat and add 1 tablespoon of oil. When the oil is hot, add the ginger slices and the onion half. Cook until the ginger is browned on both sides and the onion half is nicely browned and softened. Add the ginger and the onion to the Crock Pot or slow cooker.
When the bones have been pre-boiled, drain, discard water and rinse bones briefly to clean them. Add the bones to the Crock Pot or slow cooker. Fill the Crock Pot with fresh, clean, cool water to just 1-1/2 inches below rim, add the fish sauce and sugar. Cover and set the Crock Pot or slow cooker to cook on low for 8 hours. Taste and season with additional fish sauce if needed.
When you are just about ready to eat, you'll prep the rest of the ingredients for the Pho bowls. Bring a pot of water to a boil. Add the beef balls and cook until heated through, about 2 minutes. Remove the balls, keeping the water boiling and now cook the noodles according to package instructions. If you are using fresh noodles, all they need is a couple of minutes. Drain immediately.
Strain the stock with a fine meshed sieve. Discard the solids.
Line up 4 large bowls on counter. Distribute the noodles, beef balls and thin steak slices evenly amongst the bowls. Ladle the hot Pho stock into each bowl. The hot stock should cook the thin steak slices. Serve with lime wedges, fresh herbs, chili peppers, Hoisin sauce and Sriracha hot chili sauce at the table.