This word, as reported by Clarissa and by Spanish people on my facebook feed, makes no sense, feminist or not. Let's review the morphology here.
porta + voz falls seems to fall into the morphological category of 3rd person verb + noun. These nouns are masculine and invariant for singular and plural.
Usually, the noun is plural, like "el sacacorchos" ["removes corks"]. In the plural "los sacacorchos." The cork remover or the can opener (abrelatas). There are many such words, like aguafiestas (throws water on the party, the spoilsport.). Some refer to people, like "perdonavidas," [bully.].
But portavoz uses the singular form. The curious thing, though is that the word voz is feminine. The idea that we could make it more feminine by saying "voza" is stupid beyond belief. The noun is masculine because of the morphological pattern, not because of the word voz. Why don't we just use the elegant solution and say "la portavoz" [the spokesperson in female gender] instead of "el portavoz."
We don't say "persono" or "víctimo." Certain nouns just don't correspond to the gender of the person we are talking about. Or "Juan es buena gente."