What is the etymology and glyph origin of 餵?
喂 means feed(verb) originally besides answering telephone. 

Regarding the origin of the character, according to CiYang

(1) (餵、喂是近代的“餧”字) 喂食    餵 and 喂 are modern writing of 餧
餧,饲也。——《玉篇》    餧 means feed(verb)


It's a new character derive from 餧.

P.S. The most popular usage of 喂 may be a character for answering phone. But it is also a derivative from the common usage of saying hello in a rude way.  Because of this, in fact, there are many people claims that answering phone with 喂 is impolite, we'd better say 你好/您好 instead. If you call public service number like customer service hot lines, you always hear the operator answering 您好.