Phlegmacium boreidionysae is a species of fungus in the family Cortinariaceae.

[1] It was originally described in 2014 by the mycologists Ilkka Kytövuori, Kare Liimatainen, Tuula Niskanen, and Balint Dima who classified it as Cortinarius boreidionysae.

[2] In 2022 the species was transferred from Cortinarius and reclassified as Phlegmacium boreidionysae based on genomic data.

[3] The specific epithet boreidionysae refers to its close relationship to C. dionysae, and its boreal distribution.

[2] Found in Finland, it grows in northern boreal forests of predominantly Norway spruce (Picea abies).