Fibrous phosphorus is one of the known crystalline allotropes under standard pressure conditions. It has been predicted prior to its successful synthesis and structural characterization. The allotrope consists of parallel, tubular double strands of phosphorus, in contrast to the violet form of Hittorf's phosphorus, where the same strands are arranged in a perpendicular orientation towards each other. This structural similarity results in an almost identical energetic stability leading to a somehow problematic realization of single-phase materials. We herein report on the successful synthesis route to single phase fibrous phosphorus and the in situ characterization of its formation via the gas phase applying CuCl2 as a mineralizer. The sublimation pressure of fibrous phosphorus is slightly lower than the one of the black allotrope. This behavior indicates thermodynamic stability of fibrous phosphorus.