Ques 1:why is the resonance energy in phenol greater than benzene...
Ques 2:what does it mean to say a compound is coplanar?

1. You have electrons from the OH group which also get delocalised in the case of phenol. More delocalisation means higher resonance energy.

2. When a compound is coplanar, it means that all it's atoms are in the same plane. For example, benzene is coplanar. You can have awesome pictures if you Google benzene molecule. In contrast, methane, methyl benzene are not co planar because of the SP3 hybridization of one carbon atom, that attached to the three H atoms in methyl benzene.