Graphene can be produced with chemical method and this process goes through the formation of an oxidative form of graphene, called graphene oxide (GO), useful for mass production of graphene, obtained by reduction. Interestingly, graphene oxide is dispersible in water due to its hydrophilic functional groups and this allows the formation of liquid crystal phases above certain threshold concentration. GO shows a discotic nematic phase above a certain concentration threshold. Due to the diversity of GO flake average size, as a result of variations in production methods, the value of the threshold and the width of the region of coexistence of the isotropic and liquid crystal phase can strongly vary from samples to samples. We have observed the appearance of a nematic liquid crystal phase at very low concentration and a co-existence region form 0.1mg/ml to 1.0mg/ml by final GO obtained from synthesis. We have controlled the size of the flakes by ultra-sonication. With smaller flakes the transition concentration shifted towards much higher concentrations since the aspect ratio of the flakes has decreased. We report a detailed study of the size distribution of the GO flakes, together with UV-VIS spectroscopic and polarized dynamic light scattering, for understanding the liquid crystal phase formation.