OK. None of the content requires voice chat. I think with that we all agree. But voice chat can be helpful in some cases. Now there are alternatives for everyone out there.

From what I gather from the OP though is that some of the EX fights require a higher level of coordination than one can expect from pugs and that instead of EXs being a middle ground between let's sleep through CT/ST and need to coordinate to phase changes coil they more heavily lean to coil instead of them being the middle ground of you can still pug them without having to worry too much about messing up some of the mechanics. To top it off the whole echo buff can really mess your day in these fights.

@givemeraptors
If you are a PS4 player start your own static and focus on people also on a playstation 4 or that have a ps vita(this is what me and my friends did). Then you can all chat via the PSN party chat.
Plumble from the f-droid.org repository is a free android mumble client. I know there is teamspeak for android as well.