Catalyzes the reversible conversion of the epoxide to 2-oxepin-2(3H)-ylideneacetyl-CoA (oxepin-CoA). 2-(1,2-epoxy-1,2-dihydrophenyl)acetyl-CoA = 2-oxepin-2(3H)-ylideneacetyl-CoA Aromatic compound metabolism; phenylacetate degradation. Activated by cAMP receptor protein (CRP), integration host factor (IHF) and by phenylacetyl-coenzyme A (PA-CoA) that prevents PaaX from binding its target sequences. Inhibited by PaaX. Mutants accumulate ring-1,2-dihydroxy-1,2-dihydrophenylacetyl lactone and are unable to use phenylacetate as a carbon source. Belongs to the enoyl-CoA hydratase/isomerase family.