Place spinach, artichoke hearts, cream cheese, sour cream, chicken stock, green onions, garlic, salt and red pepper flakes into a 6-qt Instant Pot®. Stir until well combined.
Select manual setting; adjust pressure to high, and set time for 3 minutes. When finished cooking, quick-release pressure according to manufacturer’s directions.
Stir in cheeses until melted, about 2 minutes.
Serve immediately, garnished with parsley, if desired.