We investigate the electronic properties of N-layer black phosphorus by means of an analytical method based on a recently proposed tight-binding Hamiltonian involving 14 hopping parameters. The method provides simple and accurate general expressions for the Hamiltonian of N-layer phosphorene, which are suitable for the study of electronic transport and optical properties of such systems, and the results show the features that emerge as the number of layers increases. In addition, we show that the N-layer problem can be translated into N effective monolayer problems in the long wavelength approximation and, within this analytical picture, we obtain expressions for the energy gap and the effective masses for electrons and holes along the N-layer black phosphorus plane directions as a function of the number of layers, as well as for the Landau levels as a function of perpendicular magnetic field.