  We have conducted a comprehensive investigation into the magneto-transport
properties of few-layer black phosphorus in terms of phase coherence length,
phase coherence time, and mobility via weak localization measurement and
Hall-effect measurement. We present magnetoresistance data showing the weak
localization effect in bare p-type few-layer black phosphorus and reveal its
strong dependence on temperature and carrier concentration. The measured weak
localization agrees well with the Hikami-Larkin-Nagaoka model and the extracted
phase coherence length of 104 nm at 350 mK, decreasing as ~T^-0.51+-0.05 with
increased temperature. Weak localization measurement allows us to qualitatively
probe the temperature-dependent phase coherence time {\tau}, which is in
agreement with the theory of carrier interaction in the diffusive regime. We
also observe the universal conductance fluctuation phenomenon in few-layer
black phosphorus within moderate magnetic field and low temperature regime.
