All specimens are from Kota Kinabalu, Sabah, Malaysia and collected by YW Lau. Holotype: NSMT-Co 1684, Sepangar, west of Sepangar Island (06°03'38.66"N, 116°04'0.65"E), 7 m depth. Paratypes: IPMB-C 01.00011: Sepangar II, west of Sepangar Island (06°04'7.38"N, 116°04'6.76"E), 7 m depth. IPMB-C 01.00012: Manukan, north of Manukan Island, TARP (05°58'46.1"N, 116°00'10.6"E), 12 m depth. IPMB-C 01.00013: Manukan, north of Manukan Island, TARP (05°58'46.1"N, 116°00'10.6"E), 12 m depth.

The colony consists of ~50 polyps, which are connected through thin rounded stolons with a width of approximately 0.13–0.2 mm, growing over coral rubble. Polyps are partly clustered and spaced apart irregularly (1.0–3.0 mm). Polyps retract into calyces (0.65–0.77 mm width) that are barrel shaped. Expanded polyps are 3.0–3.5 mm in width and have tentacles with pinnules that are widely spaced and arranged in pairs of 12 on either side of the rachis. No sclerites were found in any of the specimens. Polyps are brown coloured in life and whitish yellow when preserved in ethanol. Zooxanthellate.

Paratypes show variation in the number of pinnules on either side of the rachis (10–13 pairs).

Sepangar Island, Kota Kinabalu, Sabah, Malaysia. Manukan Island, TARP, Kota Kinabalu, Sabah, Malaysia.

Phenganax subtilis sp. nov. differs from P. parrini and P. marumi sp. nov. mainly in the shape of the pinnules. Phenganax subtilis does not have the plump, diamond-shaped pinnules as seen in P. marumi and P. parrini. Additionally, the colour of P. subtilis is different from P. parrini and P. marumi; brown instead of the more characteristic white-grey.

From Latin subtilis, meaning simple, subtle, plain; denoting the subtleness of the polyps blending into the reef background. Gender: masculine.