Not automatic, but the GrapheneOS dialer supports call recording out of the box.

During a call, drag your buttons and they will scroll. The call recorder is the 7th button.

We recently made it so that the call recording option is not hidden away. If there are 7 options, it's RTT that will be the last one now, and we've made the scroll bar always be visible to make it clearer to people that they can scroll there.