It is endemic to Brazil and only known from its type locality in the Serra da Bocaina National Park, São Paulo state.

[5][6] Phantasmarana bocainensis was described from a single specimen, a juvenile female measuring 67 mm (2.6 in) in snout–vent length (the holotype)[7]—as of 2004, no other individuals were known.

[7] The holotype was found concealed under a rock at the margin of a mountain stream at night.

In August 2020, researchers conducted eDNA metabarcoding to extract DNA left behind by living organisms in rivers, ponds, bromeliads, streams and puddles in southeastern Brazil.

From this sampling, they found DNA from the Phantasmarana bocainensis frog and confirmed the presence of the species.