Phenol Dissociation: O-H Bond Weaker?

[crays]

Hi, my teacher told me that the oxygen in phenol would be delocalized into the benzene ring's electron and thus, making the O-H bond weaker, thus easing the release of the H proton. But i would like to know, since a benzene consist of 3 double bonds, shouldn't the electrons from the benzene itself already occupied most of the shield, thus making it harder for any other electrons to be joined in? Wouldn't the Oxygen, O's electron be repel if they try to merge into the benzene's electron cloud?

 

[Ygggdrasil]

Try drawing resonance structures for phenol. You'll see that in some of them, the oxygen will have a positive charge and thus want to get rid of its proton. Alternatively, if you draw resonance structures for the phenolate ion, you should see that the negative charge from the oxygen gets delocalized to carbons on the ring.