The type specimen was collected from the Hoonah-Angoon Census Area in Glacier Bay National Park.

The specific epithet phaeospora refers to its brownish ascospores, a feature that is unique in the genus Sagiolechia.

The photobiont partner of the lichen is a single-celled green alga with roundish to angular cells measuring 10–14 μm.

The other species in the genus, in contrast, have trentepohloid photobionts (i.e., filamentous, multicellular green algae with a yellow to orange color).

The brownish ascospores are more or less muriform (i.e., divided by horizontal and vertical septa), and typically measure 17.8–18.5 by 9.5–10.6 μm.