Eucalyptus phenax is a mallee or shrub that typically grows to a height of 3–8 m (9.8–26.2 ft) and forms a lignotuber.

[2][3][4][5][6] Eucalyptus phenax was first formally described in 1996 by Ian Brooker and Andrew Slee from material collected by Dean Nicolle near Tailem Bend in 1985.

[7][8] The specific epithet (phenax) is an ancient Greek word meaning "imposter", referring to the fact that this species was previously known as E. anceps, now a synonym of E.rugosa.

[2][9] In 2000, Dean Nicolle described two subspecies and the names have been accepted by the Australian Plant Census:[10] This eucalypt grows in mallee scrubs and is widely distributed in the southwest of Western Australia, the south-east of South Australia and the north-west of Victoria.

It is most common in Western Australia where it occurs from near Bolgart through the southern wheatbelt to Esperance.