In astrodynamicsorbit phasing is the adjustment of the time-position of spacecraft along its orbit, usually described as adjusting the orbiting spacecraft's true anomaly.
The most basic type of phasing maneuver is simply a two-impulse Hohmann transfer which takes the spacecraft away from, and then back to, its original orbit, with the period of the transfer orbit chosen such that the time in which the spacecraft returns to its original orbit can be specified.
Orbit phasing is required for a successful approach to a space station in a docking maneuver. Here, two spacecraft on the same orbit but at different true anomalies rendezvous by either one or both of the satellites entering phasing trajectories which cause them to return to their original orbit at the same true anomaly at the same time.
Phasing maneuvers are also commonly employed by geosynchronous satellites, either to conduct station-keeping maneuvers to maintain their orbit above a specific latitude, or to change latitude altogether.