Process for preparing an isocyanate by phosgenating the corresponding primary amine in the gas phase, comprising the steps of: (i) providing a gaseous stream of a primary amine; (ii) providing a gaseous phosgene stream; (iii) mixing the gaseous stream of the primary amine from step (i) and the gaseous phosgene stream from step (ii) to give a gaseous reaction mixture while maintaining a stoichiometric excess of phosgene relative to primary amino groups in a mixing zone and conducting the gaseous reaction mixture thus obtained through a reaction zone for reaction of the primary amine with phosgene to obtain a gaseous reaction product mixture; (iv) cooling the gaseous reaction product mixture obtained after passage through the reaction zone from step (iii) by contacting with at least one stream of a quench liquid in a quench zone, where the total quench liquid used, based on its total mass, comprises organic solvents in a proportion of at most 50.0% by mass, where the remainder to 100% by mass consists of at least the isocyanate to be prepared, to obtain a mixture of reaction product mixture and quench liquid; (v) conducting the mixture of reaction product mixture and quench liquid obtained in step (iv) into a collecting zone for separation of liquid phase and gaseous phase to obtain a liquid phase comprising isocyanate and optionally solvent and a gaseous phase comprising hydrogen chloride, unconverted phosgene, unliquefied isocyanate and any evaporated solvent, with introduction of a liquid solvent stream comprising more than 50.0% by mass of organic solvents, based on the total mass of the liquid solvent stream, into the collecting zone and/or into a collecting tank for the liquid phase obtained in the collecting zone which is disposed downstream in flow direction of the collecting zone. (i) providing a gaseous stream of a primary amine; (ii) providing a gaseous phosgene stream; (iii) mixing the gaseous stream of the primary amine from step (i) and the gaseous phosgene stream from step (ii) to give a gaseous reaction mixture while maintaining a stoichiometric excess of phosgene relative to primary amino groups in a mixing zone and conducting the gaseous reaction mixture thus obtained through a reaction zone for reaction of the primary amine with phosgene to obtain a gaseous reaction product mixture; (iv) cooling the gaseous reaction product mixture obtained after passage through the reaction zone from step (iii) by contacting with at least one stream of a quench liquid in a quench zone, where the total quench liquid used, based on its total mass, comprises organic solvents in a proportion of at most 50.0% by mass, where the remainder to 100% by mass consists of at least the isocyanate to be prepared, to obtain a mixture of reaction product mixture and quench liquid; (v) conducting the mixture of reaction product mixture and quench liquid obtained in step (iv) into a collecting zone for separation of liquid phase and gaseous phase to obtain a liquid phase comprising isocyanate and optionally solvent and a gaseous phase comprising hydrogen chloride, unconverted phosgene, unliquefied isocyanate and any evaporated solvent, with introduction of a liquid solvent stream comprising more than 50.0% by mass of organic solvents, based on the total mass of the liquid solvent stream, into the collecting zone and/or into a collecting tank for the liquid phase obtained in the collecting zone which is disposed downstream in flow direction of the collecting zone.