Orbital phasing is how a satellite changes its position along its own orbit: drop slightly lower to run faster and catch up, or climb slightly higher to lag back, then return to the original altitude at the desired spot. It is the workhorse of constellation slotting and rendezvous timing.
Understanding Orbital Phasing
The arithmetic of a phasing orbit
The bookkeeping is elegant: a phasing orbit whose period differs from the target orbit's by ΔT shifts the spacecraft's along-track position by ΔT's worth of arc every revolution. Need to arrive 90° of orbit earlier — a quarter period — and willing to wait 30 revolutions? Each revolution must gain 1/120 of a period, a fraction-of-a-percent altitude difference costing metres per second of delta-v. In LEO, a kilometre of altitude offset drifts the phase by roughly a degree per day-ish timescales, which is why constellation slotting plans speak of "drift rates" and why a low-thrust satellite can phase precisely with electric propulsion alone: the offsets involved are tiny and the burns gentle.
Phasing in the wild
Watch any constellation operator work and phasing is everywhere: new satellites drift along a plane to their assigned gaps; spares parked below the shell phase into position before climbing to replace a failure; end-of-life craft phase clear of the lattice before deorbit. Cargo and crew vehicles fly phasing profiles measured in hours or days depending on how favourable the launch geometry was. Even collision avoidance is phasing in miniature — a temporary period change that shifts arrival time at the conjunction point by the fraction of a second that converts a hit into a miss. Almost every "satellite moved" story that is not a plane change or an altitude change is, underneath, a phasing manoeuvre.