Engine damage varies in cause and correction between engine models.
Basically the engine is design and certified not to be damaged from in-flight icing conditions. The presumption being that on-the ground the engine will not be dispatched with visible ice.
However, on-ground operations at low idle condition (sitting and waiting etc.) the depressed air temp inside the inlet (no-ram air) may form ice on the nose spinner, the fan blades or the compressor vane immediately behind the fan.
This ice may be shed during run-up conditions either by centrifugal forces (spinner or fan blades) or by windage effects against the compressor inlet vanes behind the fan. The RPM to effect this shedding (varies with engine model) must occur often enough that the ice that is shed does not visibly damage the engine nor affect its operation. Again even this latter effect varies with engine model.
Thus what turns up in your operating procedures may vary and is there to avoid situations shortly after aircraft rotation.