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.
Ask your users if their kids use Steam. Most of my home users have older "kids" I tell them to have their kids stop there Steam games. The users are like what's that?? But as soon as steam is stopped their perfomance comes right back to nominal.
It would be them downloading more games, most likely.