Self-Hosted Main

So, I was buying a new phone, and that phone happened to only have 1 sim card slot, the other sim is an esim (which isn't supported yet where I live), while I have dual sims that I need with me at all times. And so I thought, is there a way to host a server on my old phone (or a computer/raspberry pi/linux server) connected on the same network as that old phone, and have an app on the new one that allows me to dial a number, click on call, and in the background the server handles the request by initiating the call on the old phone, and directing mic and sound to the new one? The phones and potential server could be connected to a VPN tunnel of sorts so that the ips of all 3 devices would be static and known at all times.

It could be done with some programming, which I could do, but I'm admittedly too lazy, so I thought maybe there'd be a way to do it without? Maybe an app that already does this or anything similar? A google search didn't return anything useful, but maybe someone here knows something.