According to its Wikipedia infobox, pho is served hot.
That serving temperature fits the dish’s structure: hot broth is poured over rice noodles, herbs, and thinly sliced meat. The heat warms the noodles and can gently cook rare beef placed in the bowl immediately before serving.
Pho developed in northern Vietnam in the early 20th century and is commonly associated with Hanoi and Nam Định. Beef pho and chicken pho are the best-known versions, but both are normally presented as steaming noodle soups.
A common mix-up is confusing pho with other Vietnamese noodle dishes that may be served chilled, at room temperature, or dry. Pho may cool while being eaten, but “served” in the infobox describes its customary presentation, not the temperature of every bite.