carbocation and Electrophilic Aromatic Substitution 

Overall an electrophilic aromatic susbtitution (EArS) can be represented as follows:

There are three fundamental components to an electrophilic aromatic substitution mechanism:

1. formation of the new σ bond from a C=C in the arene nucleophile
2. removal of the proton by breaking the C-H σ bond
3. reforming the C=C to restore the aromaticity

The mechanism is represented by the following series of events:

• Formation of the reactive electrophile, E⁺ (not shown here) from the reagents
• Slow reaction of the arene C=C with the E⁺ to give a resonance stabilised carbocation (see below)
• Loss of H⁺ from the carbocation to restore the C=C and the aromatic system

The reaction of the electrophile E⁺ with the arene is the slow step since it results in the loss of aromaticity even though the resulting cation is still resonance stablised.
 This carbocation is also described as the cyclohexdienyl cation or arenium ion or as a sigma-complex. 

When phenol undergoes eas .carbo cation intermediate is formed which is stablized only at ortho and at para position.Not at meta position.