Showy phlox  
Phlox speciosa Nutt.

Collected along the Clearwater River between Pine Creek and Big Canyon Creek, Nez Perce Co., Idaho, on 7 May 1806. (Source)

Showy phlox is pretty perennial phlox with a shrubby base, with multiple stems which may rise from 15 to 40 cm high. The herbage is glandular to glandular-hairy above. The leaves are linear to broadly lanceolate, and to 7 cm long and 1 cm wide. The leaves are opposite on the stems, and are widely spaced. The inflorescence is a loose cyme. Individual corollas are pink to white, usually with notched petal tips. The tube is 10 to 15 mm long, with the lobes an equal length. The calyx is about equal in length to the tube. The membranes between the calyx ribs are flat to slightly keeled. The style is very short (0.5-2 mm long) and is divided near the base into 3 linear stigmas which are longer than the style.

Showy phlox is a wildflower of sagebrush and ponderosa pine habitats. It is found in the northwestern states and eastward into Idaho and Montana. 

(Source)