Mormonilla phasma is redescribed, based on the specimens from the Northeastern Pacific. M. phasma in the study area has the following morphological characteristics; second endopodal segment of mandible partly fused to basis and a distinct three-segmented exopod of mandible in anterior view and one indistinct segment in posterior view which are different from the description given by Boxshall (1979). In addition the first and the second endopodal segments of leg 1 were also separated indistinctly. Other morphological characteristics are similar to those reported in previous studies. The morphological anomalies in endopodal segments of the leg 1, unknown up to now are also discussed. This study is the first report on the distribution of M. phasma in the Northeastern Pacific.