Phased Munitions are a booster to projectile weapons. They are the counterpart of phased projectiles for ship weapons. They increase shield bypass, hence more damage is allocated to the target's armor than the shields. This is useful in that attacking fleets are permanently debilitated and weakened for their next battle, hence, they must retreat and repair if they want to return to full strength.
Phased Munitions work well with Gladius driver turret or AP driver turrets used in combination with Arrestor beam turrets, effective at defending the base against long range attacks. The speed and proximity detonation of Gladius driver turrets allows the projectiles be already fast enough to strike targets rather easily. Arrestor Beam Turrets help by hindering a ship's movement, particular decoy ships, allowing even Kinetic driver turrets with phased munitions to land s hit on their opponents with some ease.
They are very light weapon booster and somewhat common amongst bases. On level V bridges equipped with a projectile turret, it would most certainly have both Iridium arrays and phased munitions.