The newer versions of OS X hid a few key system features, including the Character Viewer and Phonetic Alphabet list item therein. Below are the steps to first enable the Character viewer, then enable the phonetic characters, in OS X Yosemite.
Enabling the Character Viewer:
The Character Viewer will now be present in the menu bar as shown below:
Enabling the Phonetic Alphabet Characters:
Article ID: 481
Last updated: 02 Aug, 2016