the top on the phenoms is less arched than that of the wisdoms... so if its like a skate style helmet phenoms fit perfectly but maybe not as well on most giros i would think but im not positive
They should fit real nice! Phenoms are some of the most comfortable goggles i've ever worn, I lost my giro helmet awhile back, otherwise I'd totally go try it on with phenoms and tell you what its like, but I think you'll be good to go.