When discovered in the 19th century and during the following decades, Phlaocyon was thought to be ancestral to raccoons because of shared convergent adaptations toward hypocarnivorous dentitions, but Hough 1948 was the first to discover the canid nature of the middle ear region in P. leucosteus and Phlaocyon in now believed to be part of very diverse clade of hypocarnivorous canids, the Phlaocyonini, and only distantly related to raccoons.
P. mariae and P. yatkolai, both known from isolated teeth and fragmentary material, are the largest and most derived species, and both display a tendency away from the hypocarnivorous dentition of the genus and towards a more hypercarnivorous dentition.
Phlaocyon was about 80 centimetres (31 in) in body length, and looked more like a cat or raccoon than a dog, but its skull anatomy shows it to be a primitive canid. Phlaocyon probably lived like a raccoon, often climbing trees. Its head was short, wide, and had forward-facing eyes. Unlike modern canides, Phlaocyon had no specialised teeth for slicing flesh. It is thought to have been an omnivore.
Legendre & Roth 1988 estimated the body mass of two specimens to be 1.81–1.87 kilograms (4.0–4.1 lb).