Here's why:

* FeCl3 (ferric chloride) is the reagent used to identify phenols. FeCl3 reacts with phenols to form colored complexes, typically violet or purple. This reaction is based on the formation of a complex between the ferric ion (Fe3+) and the phenolic hydroxyl group (-OH).

* FeCl2 (ferrous chloride) lacks the necessary oxidizing power to react with phenol in the same way that FeCl3 does. The ferric ion (Fe3+) is a stronger oxidizer than the ferrous ion (Fe2+). This difference in oxidizing power is crucial for the reaction with phenols.

In summary, FeCl2 is not used to identify phenol because it does not react with phenol to produce a characteristic color change.