In 3-quart saucepan, place potatoes and garlic; add enough water to cover. Heat to boiling; reduce heat. Cover; simmer 15 to 20 minutes or until potatoes are tender. Drain potatoes, reserving cooking liquid.
In saucepan, mash potatoes, garlic, parsley, salt and pepper with potato masher just until lumpy. Gradually add about 1/4 cup cooking liquid, mashing until combined but still lumpy. Stir in sour cream.