Add the broth, rice, onions, and celery to the pressure cooker pot.
Set the manual cook time for 35 minutes.
Let the pressure release naturally while you make the white sauce.
On the stove top, melt the butter in a saucepan over medium heat.
Whisk in the flour and cook for a minute.
Gradually mix in the milk. Cook over medium heat until it's bubbly and thickened. Add the poultry seasoning, salt and pepper.
Release any remaining pressure in the Instant Pot. Stir in the white sauce. Stir in the chicken.
Hit the saute button and cook until heated through. Adjust the seasonings and serve.