Disclosed are an optical modulation device and a phase modulation method using the same. The optical modulation device includes a reflection plate, an insulating film over the reflection plate, dielectric patterns aligned on the insulating film in a first direction and extended in parallel in a second direction intersecting the first direction, and first and second graphene patterns provided between the dielectric patterns aligned in the first direction and arranged in an alternating fashion. The first and second graphene patterns are in direct contact with the insulating film and the dielectric patterns are in direct contact with the insulating film at locations between the first and second graphene patterns. A width of each of the first graphene patterns in the first direction is different from a width of each of the second graphene patterns in the first direction.