if your primary concern is "big brother" even dumb (mobile) phones won't help you b/c big brother is taping in at the cell level, that is the GSM / 4G antenna "FROM YOUR PROVIDER"
short of using VoIP w/ encryption.there is ##NO## privacy when making phone calls
NADA
Skype uses a ##PROPRIETARY## protocol to encode its VoIP traffic
see this for an explanation about Skype security concerns ( https://en.wikipedia.org/wiki/Skype#Security_and_privacy )
remains Zfone ( http://zfoneproject.com/index.html ) but... unless you r heavy in coding / debugging this isn't a real option neither
or Linphone ( https://en.wikipedia.org/wiki/Linphone )
as far as privacy on your device... well, unfortunately the only safe bet is a FOSS (Free Open Source SW) device, thus in your list the Jolla phone with Sailfish OS (or one of its predecessors Maemo or MeeGo )
alas, neither of the three is supported by Linphone (exceept,indirectly Jolla which has announced seamless support for Android Apps).
==> Jolla is your solution
but at the end of the day the biggest "risk" for your privacy / security is your own (reckless) behavior.
even if big brother can't listen in on your encrypted VoIP conversations / chats (that's assuming the other party doesn't use some Android or (i-)Crap device (with all due respect to NOKIA) in which case, well, forget abut any security as NSA (at least) can tap into any US corporation's data...) the simple fact of having a GSM-Sim (or connect to a wi-fi) makes you immediately identifiable thanks to the Mac-addresses of each
think about John Connor at the beginning of Terminator 3 / Rise of the machines...
«I should feel safe, but I don't, so I live off the grid - no phone, no address, no one and nothing can find me. I've erased all connections to the past [...]»
EDIT: Jolla announced that they have made Sailfish OS compatible with most hardware usually found in Android device
their primary aim is to make it easier for Android device manufacturer to offer Sailfish as an alternative OS.
this however is not FOSS anymore as there (very likely) won't be any real insight in what the manufacturer does with the FOSS code.
thus the only "safe" bet will be to install a "free version" of Saiflish OS onto an Android device oneself.
it is possible nowadays to install Android onto Maemo / MeeGo devices (see Nitdroid http://www.nitdroid.com/ ) but Sailfish OS on Android devices remains to be seen...
EDIT2: chinese (government) hackers have been shown to be able to hack into (even fairly well secured) US corporate networks, thus...