just patch inputs and outputs to audacity (or your recording software of choice). for pipewire theres helvum[0] or qpwgraph[1]. for JACK there's Catia[2].
If you have a headphone jack and a splitter that could work. I do not know of any "two sided" Bluetooth devices that could sit between a phone and headset.
Either that or use a computer to do the call and record using software on the computer.
I don't know how the latter is done but I know many companies do that.