[3]: 204, 206-208  Phaeacius is very well camouflaged;[1] for example, P. malayensis has a body with dull grey and brown markings that resemble the surface of tree trunks in the rainforest.

[6]: 53 Spiders, like other arthropods, have sensors, often modified setae (bristles), protruding through their cuticle ("skin") for smell, taste, touch and vibration.

[16] Unlike most jumping spiders, Phaeacius and other spartaeines do not leap on prey, but lunge from about half the predator's body length away.

[5] Phaeacius is unusually sedentary for a jumping spider, generally resting in the flattened pose for hours or days on logs, pieces of wood or any other solid surface,[2]: 502  and captures particular types of prey more often when the predator matches this background.

To rock, Phaeacius moves about half a body length forward then, without pausing, smoothly back almost to the previous position.

[5] Other jumping spiders show no awareness of a flattened Phaeacius on a matching background, and apparently survive by luck.

Often Phaeacius then adopts the flattened pose after the turn, but sometimes it walks faster than usual and, without pausing, lunges from about half its body length.

[5] Phaeacius does not try to eat other spiders' eggs, does not enter webs voluntarily, and moves away if it touches one accidentally.

[2]: 502  This behaviour is quite different from that of its close relative, Portia, which hunts actively and can enter any type of web to catch spiders and their eggs.

[2]: 499–500 Before courtship, male spiders spin a small web and ejaculate on to it, and then store the semen in reservoirs on his pedipalps,[18]: 581–583  which are larger than those of females.

[18]: 572–573  Phaeacius spins a flimsy silken, horizontal or vertical platform, about twice the spider's length in diameter, to moult and lay eggs, but not at other times.

[19]: 236 The genus is found in subtropical China[9] and between India and Malaya,[1] including Sri Lanka, Sumatra and the Philippines.