Set the Instant Pot to the 'Sauté' function. Add the halved onion, crushed garlic cloves, and sliced ginger. Cook for about 3-4 minutes until fragrant and the onion is slightly charred.
Toss in the cinnamon sticks, star anise, and cloves, cooking for another minute to toast the spices.
Add the chicken thighs, chicken broth, fish sauce, sugar, and salt to the pot. Stir to combine the ingredients.
Close the lid, set the valve to sealing, and cook on high pressure for 15 minutes. Once complete, allow a natural release for 10 minutes before performing a quick release.
Open the lid and carefully remove the chicken thighs. Shred the chicken using two forks and return it to the pot.
Stir in the rice noodles and let them soak in the hot broth for about 5-7 minutes, or until al dente.
Ladle the pho into bowls. Top with fresh basil, chopped cilantro, lime wedges, and bean sprouts. Add sliced jalapeños for extra heat if desired.