Quasi-one-dimensional (QID) semiconductor materials, such as carbon nanotubes, SbSI, MP15 (M = Li, Na, K), and selenium and tellurium nanowires, show amazing potential for applications in future nanoelectronic and optoelectronic devices. However, intricate chirality in the structure of carbon nanotubes limits their applications. Also, the performance of MP15 in optoelectronics has yet to be extensively explored. One new Q1D semiconductor material, fibrous phosphorus (FP), has recently received attention because its raw material is less toxic. However, the ability to characterize FP by phase identification is limited in the assessment of micro/nano-thickness, such as exfibrated FP. So, identifying a precise Raman spectrum will allow for much better characterization. Here, a sufficiently sharp Raman spectrum of FP was obtained and analyzed. Moreover, we demonstrated that high-quality, few-layer FP fibers with thicknesses as low as 5.55 nm can be produced by liquid-phase exfibration under ambient conditions in solvents. More importantly, an optoelectronic detector based on a single FP fiber field-effect-transistor configuration was investigated. A rise time as short as about 40 ms was obtained for the FP transistors, illustrating the potential of FP single bundle crystals as a new one-dimensional material for optoelectronic device applications.