What makes phenol different from alcohols?

You will need an underlying knowledge of the structure of benzene to answer this question. Benzene (C6H6) is formed from 6 carbon atoms arranged in a ring. [draw benzene] Each carbon atom has 4 bonding electrons (because it is in group 4), 2 of these are used to bond to the adjacent carbon atoms and 1 is used to bond to the outer hydrogens, leaving 1 electron remaining in a p orbital. [draw] This orbital overlaps either above or below the plane, similar to an alkene double bond, and the electron becomes delocalised, forming a pi bond. The difference between benzene and ethene (for example) [draw] is that in benzene the delocalisation occurs all around the circle of carbon atoms, forming a circular pi bond. [draw]

This same effect can be seen in phenol, whereas this time 2 more electrons (sourced from the oxygen atom) [draw] are able to be delocalised into the ring. The overall effect of this delocalisation is an extremely electron dense, nucleophilic centre. Meanwhile the oxygen atom itself actually has a lower electron density in phenol than it would in an alcohol because it has donated them to the ring. This leads to phenol having different properties to alcohols, the main one being that in solution (with water) the hydrogen from the OH group dissociates to form a weak acidic solution. This can then be neutralised to form salts or other products.