The objective of the phonetic alphabet is to convey exact information by spelling. It’s purpose is to allow things like coordinates, codes, locations, etc, to be transmitted without loss of information over noisy communication lines, like radio. We don’t want to use it to pass full sentences, just very specific info that we wish to be lossless.
EDIT: to give an example the letters P, T, D and others all sound the same over noisy lines, so we use Papa, Tango and Delta, that are very distinct words.
Learned it in the army (I was in engineering specialized in comms, so…) and later used it in airsoft. My airsoft callsign was actually Sierra because videogames. I admit it does bring some memories. 
For more info: https://en.wikipedia.org/wiki/NATO_phonetic_alphabet