Add the slices of tofu/fried tofu and Vietnamese sausage if using to heat them through. Add a tsp of vegetable oil to the broth if you're not adding fried tofu. The small about of oil adds a richness to the broth.
Meanwhile, cook the pho noodles until al dente (so when you add the steamy broth, they're perfectly chewy and delicious!), drain and segment into servings. It's easier to do this when they're freshly cooked, otherwise they'll drain into one big clump and be hard to divide.
Remove everything but the mushrooms from the pot. Start seasoning the broth with mushroom broth powder (or salt), vegan fish sauce, yellow rock sugar, MSG, and vegan beef bouillon cubes. Start out a little of each ingredient at a time until you have the full-bodied broth you like.
Pour broth over pho noodles, garnishing the tofu, sliced mushrooms (from the broth), vegan Vietnamese sausage, culantro leaves, Thai basil, bean sprouts, cilantro, green onion and a squeeze of lime. Add hoisin sauce and sriracha to taste!