Heat oven to 400° F. Place the garlic on a sheet of foil and drizzle with the oil; fold and seal to form a pouch. Roast until tender, 40 to 45 minutes; unwrap and let cool.
Squeeze the garlic cloves from their skins and place in a food processor along with the cream cheese and milk and puree until smooth. Transfer to a medium bowl and stir in the scallions, ½ teaspoon salt, and ¼ teaspoon pepper. Serve with the bagel chips.