Select the "saute" setting on the Instant Pot.
Once it reads "hot" add butter and let melt.
Add in onions and celery and saute 2 minutes then press "cancel."
Add in potatoes, carrots and broth and season with salt and pepper to taste. Submerge veggies down into broth.
Seal lid on Instant Pot, make sure valve is set to "sealing position," then select "manual" mode and 9 minutes.
Once time is up let pressure come down naturally for 5 minutes then use quick release method to release any remaining pressure.
In a medium bowl whisk a few tablespoons of milk with the cornstarch then add in remaining milk and whisk.
Press "cancel" on Instant Pot then select the "saute" setting.
Pour milk mixture into soup in Instant Pot along with cream cheese.
Bring mixture to a boil, whisking frequently, and let boil about 1 minute (you can also mash up the potatoes a little if desired).
Serve warm with cheddar, bacon, and green onions or parsley. Note that soup will thicken as it rests (especially overnight with all those starches, so thin with more milk as desired).
Recipe source: Cooking Classy