The simplest way is to prop your phone up somewhere securely and put it on speaker phone. The select record, I think on my phone it is called something like voice memo.
There are facilities on most phones to directly record calls, you would probably get a better quality of recording. If you let us know what sort of phone you are going to use someone in our community might be able to advise you.
Oh, and however you decide to do it, have a few practice runs first! Catherine
Nothing on this board constitutes legal advice - always consult a professional about specific problems