R package phaseR: Phase Plane Analysis of One and Two Dimensional Autonomous ODE Systems. phaseR is an R package for the qualitative analysis of one and two dimensional autonomous ODE systems, using phase plane methods. Programs are available to identify and classify equilibrium points, plot the direction field, and plot trajectories for multiple initial conditions. In the one dimensional case, a program is also available to plot the phase portrait. Whilst in the two dimensional case, additionally a program is available to plot nullclines. Many example systems are provided for the user.