The Phase Shield is a Special Module found on Guard frigates. The Phase Shield can be attuned to one of the three types of damage: EM, Kinetic, or Thermal, and provides extra shielding against that particular type. Upon receiving that particular type of damage, the main ship's weapons are boosted for a short period of time. This special module is always on, and activating it will only change the type of damage that it is attuned to. The default setting is for thermal, and cycles through thermal, EM, and kinetic.
Thermal is represented by a red symbol, EM by blue, and kinetic by yellow.