RNA/Protein (RNP) Bodies are membrane-less intracellular organelles associated with a variety of biological functions. We have shown that several of these structures exhibit liquid-like properties, and may represent droplets of phase-separated protein and RNA. The nucleolus is a liquid-like RNP body which plays an important role in cell growth and size homeostasis. Using the reductive cell divisions of early C.elegans embryos, we find that the nucleolus exhibits size scaling, with larger nucleoli assembling in large cells and smaller nucleoli in small cells. Surprisingly, however, when embryo size is altered, we observe inverse scaling: nucleolar size increases in small cells and decreases in large cells. We demonstrate that this seemingly contradictory result can be explained with a simple critical concentration model, suggesting that the physics of phase transitions dictates both whether an organelle assembles, and if so, its size. Since the nucleolus is a key organelle for cell growth, this biophysical read-out of cell size could provide a novel feedback mechanism for growth control.