A method for manufacturing molten steel containing low-phosphorus using finex hot metal is provided to use decarbonization slag as a material instead of quicklime in order to protect a furnace and reduce manufacturing cost by reducing the amount of quicklime to be used as a material. A method for manufacturing molten steel containing low-phosphorus using finex hot metal comprises the following steps. Fine iron ore is reduced using fluidized reduction furnaces(3,4,5) and inputted into a melting furnace to manafacture a hot metal. A furnace is coated with decarbonization slag. Finex hot metal and scrap iron are inputted into the furnace. The finex hot metal is smelted. The smelted finex hot metal is pulled out. The basicity of decarbonization slag is from 6.5 to 7.5.