Eucalyptus × phylacis is a tree or robust mallee, that typically grows to a height of 5 m (16 ft) and forms a lignotuber.

The fruit is a woody, hemispherical capsule 5–6 mm (0.20–0.24 in) long and wide with the valves strongly protruding.

[2][3][4] Eucalyptus phylacis was first formally described in 1992 by Lawrie Johnson and Ken Hill in the journal Telopea from a specimen collected on the east side of Cape Naturaliste in 1983.

[4][5] In 2012, Dean Nicolle suggested that this species is a hybrid between E. decipiens and E. virginea and that although it flowers profusely, it does not produce viable seed.

[6] The Australian Plant Census lists Eucalyptus × phylacis as an accepted species but a hybrid.