Phew! Busy couple of days for me. Sorry for the late reply.
OK, so the setup is as @JaredBusch assumed. VPN on the Laptop only. Split tunneling was not enabled and now it is. Problem solved for now! DuckDNS is reporting the correct home IP. No need for VPN on the phone or PBX.
Good call @Dashrender
@scottalanmiller I'm still going to checkout the possibilities of OpenVPN though. Just in case I need it in the future.
Thanks guys. Have a great weekend.