Phasia obesa is a species of 'parasitic flies' belonging to the family Tachinidae subfamily Phasiinae. This fly is present in most of Europe. The adults grow up to 4–6 millimetres (0.16–0.24 in) long and can mostly be encountered from June through September feeding on nectar of flowers (especially of Asteraceae species). Their large compound eyes are reddish. The body is greyish, with four longitudinal black bands interspersed with clear bands of the same thickness on mesonotum. The large wings show a light brownish shading. The cell R5 is closed at the edge.