REKK is the best app to record calls on the iPhone from a function point of view.
On the occasion of a phone call, simply open the app and touch the recording button generated by the application to start recording.
TapeACall is one of the most used and known applications in the world to record calls on the iPhone.
The big advantage of iCall is the ability to record incoming and outgoing calls on iPhone literally with a single tap.
The secret lies in the UI, made for easy use even by the elderly or those not so accustomed to technology.