How can I record a phone call on my iphone so it saves to the drive and not iCloud?

I need to record phone interviews for a research project. My institution requires that recordings cannot be on a cloud aside from their own due to data safety with sensitive data. I want to use the record function on iPhone to record (and ideally transcribe) the calls, but I can only do it if I can get it to NOT save to iCloud at all. I can't find a setting to change where it saves.

I know I can do this with zoom, but my participant group needs a 100% optimal non-PITA option.