Add 1 cup water to instant pot. Add cauliflower in steamer basket or directly in water (steamer basket makes it easier to drain) Seal, program for manual, high, and decrease time to 8 minutes.
When cook time ends, select either natural pressure release or quick release. Drain water. Using an immersion blender, puree cauliflower.
Add cream cheese, salt, and pepper. Puree again with immersion blender until cream cheese is melted. Add butter and stir to melt if desired.