Add the avocado oil to the Instant Pot and select the Saute button. Once the pot is warm, add the onion and apple (both cut-side down), ginger, cardamom, cinnamon stick, star anise, and cloves. Saute the food until slightly charred, approximately 4 minutes.
Turn off the Instant Pot. Without removing anything, add the beef bone broth, chicken stock, fish sauce, sugar, and salt. Place the lid on the Instant Pot and select Soup/Broth for 20 minutes.
While the broth is cooking, prep your toppings.
When the Instant Pot is done, let the pressure naturally decrease for 10 minutes. Then carefully open the Instant Pot.
Using a slotted spoon remove everything from the pot except for the Pho broth. Or you can strain and add broth back to the pot.
Get individual bowls ready. Add noodles to each bowl and top with soup.
Top with thinly sliced flank steak (which will cook in the hot broth). Then top with bean sprouts, bok choy, and radishes.
Serve pho along with a plate of basil, cilantro and lime wedges, as well as sriacha and hoisin sauce.