Long-leaved phlox is a beautiful erect phlox arising from a woody base to a height of 40 cm on weak stems. It frequently is somewhat hairy or glandular, especially within the inflorescence. The leaves are linear, ranging in length from 15 to 80 mm long and 1 to 3 mm wide. The leaves are widely spaced along the stems, and are opposite each other.

The inflorescence is a loose cyme, with several 5-petaled, sweet-scented flowers at the apex of the stem. The corolla is typically white or pink, with the tube being about 10 to 18 mm in length. The lobes of the petals are spreading, about 7 to 15 mm long, and obovate in shape. The calyx is 1/2 to about as long as the tube. The membranes between the 5 prominent ribs on the calyx are prominently keeled or bulged outwards near the base. The style is elongated and ranges from 6-15 mm long. The 5 anthers are arranged with 2 near the mouth of the tube, 2 directly below, and a 5th further below near mid-tube (See photo below.).

Long-leaved phlox is found from dry open rocky or sandy places in the lowlands to moderate elevation in the mountains.

Long-leaved phlox is found from southern British Columbia south along the eastern slopes of the Cascades to southern California, and eastward to the western slopes of the Rocky Mountains of Montana, Wyoming, Colorado, and New Mexico.