Add the chicken to the Instant Pot on top of the charred onion and ginger. Add the Pho spice bag, fish sauce, and sugar. Add the Quoc Viet Foods Chicken Flavored Pho Soup Base (if desired, optional).
Fill the Instant Pot with water to the max fill line.
Cover and program the Instant Pot to "Manual" high pressure for 30 minutes. Then let it naturally release for 20 to 30 minutes.
Using sturdy tongs, remove the chicken to a cutting board. (Be careful - the meat will be falling apart). When it's cool enough, shred the chicken.
Remove the onion, ginger, and pho spice package. Taste and add more fish sauce, if desired.
When you're ready to serve, press "Saute" on the Instant Pot.