In the first GC columns, gas chromatography phases were simply coated onto the column. This was mostly the case with packed columns, but also the same with the very first capillary columns. Injecting water onto these phases dissolved the phase and caused the phase to elute from the columns.
The boiling point is the temperature where liquid has enough energy that molecules transferring into the vapor phase exert a pressure that is equal to the outside pressure. This allows molecules anywhere—not just the surface—to transfer to the gas phase.