Phlox diffusa is a species of phlox known by the common name spreading phlox. It is native to western North America from British Columbia to the southwestern United States to the Dakotas, where it grows in many types of habitat, including rocky, high elevation mountain slopes. It is a very compact mat-forming perennial herb growing in cushions or patches of short, decumbent stems. The linear, lance-shaped, or needle-like leaves are no more than 1.5 centimeters long and are oppositely arranged in bundles on the short stems. The inflorescence is a solitary tubular flower around a centimeter long. It has a flat white or pale pink or blue corolla with five lobes each just under a centimeter in length.