There are generally four main moving parts to a bowl of pho: the broth, the noodles, the meat, and the garnishes (bean sprouts, basil, cilantro, lime, and chili peppers are common). The broth and the meat for phở is generally beef, though depending on how strict you want to be in your definition of the term “pho,” there are versions involving chicken, duck, pork, and various seafood, as well. Even the seafood-based bowls often feature a beef broth built by lovingly simmering bones, oxtails, and the undesirable parts of the cow for many hours.
But pho broth is far more than a stock, rich and long-simmered as it is. It owes its ethereal flavor profile to charred ginger and onion, on the one hand, and a bevy of aromatic herbs and spices -- particularly cinnamon, star anise, cardamom, black pepper, and cloves -- on the other.
Most phở uses flat rice noodles. (Indeed, the word “pho” is likely a corruption of the Cantonese word phaan meaning “flat rice noodles.”) It's no accident that the name of the dish is also the name of the noodles (“banh pho”). While the choice of protein usually determines the name of a bowl of pho, at the end of the day, pho is a noodle dish -- not a meat one.