Acrophony

Acrophony refers to naming letters in an alphabetic writing system using words whose initial sounds (Greek: acro uppermost, head + phonos sound) are represented by the respective letters. For instance, were the English alphabet named acrophonically, the letter "A" might be named "axe" or "aardvark" or any other word beginning with A.
See more at Wikipedia.org...

Noun
1. naming a letter of the alphabet by using a word whose initial sound is the sound represented by that letter
(hypernym) naming

(n.)
The use of a picture symbol of an object to represent phonetically the initial sound of the name of the object.