Mobile carriers here are bringing back NAT on ipv6 now. Wannacry fears? NAT for the sake of firewalling? Phones still seem to get individual addresses.

Which one? Really curious. Another point to mention, that I've seen mobile operators sends you multiple /64s, thus if you run in adnroid shell 'ip addr' you see one /64 while if you connect say to ripe.net it shows completely different IPv6 address from different range, while still no NAT. Perhaps that was your case, perhaps not. Details would be very interesting.

If your address on ripe.net doesn't match any of your local interface addresses, then that's NAT (or perhaps a transparent proxy) by definition.

Well, in some environments, it's possible to bind() to an IP address that's not actually present on a local interface, but it's unlikely that your browser would support that.

On other side I can ping IPv6 address of the tethered laptop. And for tethered devices ripe reported IPv6 matches interface. Indeed, transparent proxy / media gateway could be the case for the phone itself.

If anyone sees a mobile provider does this, please complain loudly.

You might be interested in Syncthing (syncthing.net). It works a bit like BitTorrent Sync, is open source and does support IPv6 (of course).