interjection, to call attention
喂 centers on vocal interjection: a call to get someone's attention, like saying "hey" or "hello" to initiate contact.
喂 combines 口 (mouth) with 畏, which likely contributes a phonetic element. The character is used for interjections and calling attention, fitting the mouth radical.
The mouth 口 on the left and the distinctive shape 畏 on the right suggest a mouth making a call. Picture someone cupping their mouth and shouting "喂!" to get attention.
For イ, imagine calling out "E!" (like the letter E) to get someone's attention: E -> イ, and the mouth 口 is wide open.