Phlegmacium is a genus of fungi in the family Cortinariaceae.

[1] The genus was created in 1877 by the German mycologist Friedrich Otto Wünsche[2] based on the earlier 1821 classification of the Agaricus tribe Phlegmacium by the Swedish mycologist Elias Magnus Fries.

[3] In 2022 the family Cortinariaceae, which previously contained only the one genus of Cortinarius was reclassified based on genomic data and split into the genera of Cortinarius, Aureonarius, Austrocortinarius, Calonarius, Cystinarius, Hygronarius, Mystinarius, Phlegmacium, Thaxterogaster and Volvanarius.

Numerous Cortinarius species were transferred into the genus of Phlegmacium as a result of this work.

[4] The genus is further divided with subgenus and section classifications:[4] As of January 2023, Species Fungorum accepted 252 species of Phlegmacium.