Mix together potatoes, cream cheese, butter, sour cream and milk. Beat until smooth.
Put a liner in a slower cooker and pour potatoes in. Cool completely.
Close bag with a twist tie and place in the refrigerator for up to 3 days.
Heat on low for 3 hours until warmed through, stir often to help heat evenly. Add pats of butter, milk or dollops of sour cream as needed to keep creamy and moist.
Once warm turn down to keep warm. Continue to stir occasionally until done serving.