The effects of analyte phase on the calibration response for laser-induced breakdown spectroscopy is investigated for a range of carbon species. Significant differences in the atomic emission signal from carbon were observed when comparing calibration streams of gas-phase and submicrometer-sized solid-phase carbon species. The resulting calibration curve slopes varied by a factor of 8 over a comparable range of atomic carbon concentrations for five different analyte sources, while the plasma electron density and temperature remained essentially constant. The current findings challenge a widely held assumption that complete dissociation of constituent species within a highly energetic laser-induced plasma results in independence of the analyte atomic emission signal on the analyte source. A physical model of the plasma-analyte interaction is proposed that provides a framework to account for the observed dependence on the physical state of the analyte.