The control of spin transport is a fundamental but crucial task in spintronics and realization of high spin polarization transport and pure spin currents is particularly desired. By combining the non-equilibrium Green's function with first principles calculations, it is shown that halogen adsorption can transform a black phosphorene monolayer from a nonmagnetic semiconductor to a magnetic semiconductor with two almost symmetric spin-split states near the Fermi level, which provides two isolated transport channels. Further investigations demonstrate that a device based on halogen-decorated phosphorene can behave multifunctionally, where a pure spin photocurrent and a fully spin-polarized photocurrent can be effectively controlled by tuning the photon energy or polarization angle of the incident light. In addition, pure spin current can also be induced by a temperature gradient, resulting in a perfect spin Seebeck effect. This work demonstrates that the halogen-decorated phosphorene systems have potential applications of high integration density and low energy dissipation in two-dimensional spintronic devices.