I’m sure not many wants to give their phone number out. Perhaps if the devs make a discord, more would be willing to do a voice survey there.
Schedule an appointment time for the survey with a dev and meet there.
I dont think they will do many phone calls. Maybe 3 or 4 for some surveys with extreme views. Phone calls are time consuming.
I‘m VERY excited they are offering this. I really hope they get sensible feedback from this. I am certain many of their players can provide that, so it might really not take many calls.
Getting a phone number is also more personal than „anonymous voice chat“. They might reduce offers from players that only want to speak anonymously this way, which I would understand.
would love to read here of players that get the feedback offer, but probably they will need to sign an NDA.
If they want to chat with me, I am more than happy to give out my phone number. What exactly bad thing would happen if D3 got my phone number? They might sell it so I get more spam calls? I already get plenty so a few more won’t hurt me.
Maybe we could just post our phone numbers here and say “ Call Me !” 
As a heads-up, if you select “Yes you can contact me by phone” they don’t ask for a phone number through the survey - just an email address. Presumably they’ll contact you with further information via email if they decide that they want to talk to you whenever the survey data is collated.