When you call someone, The record button isn't available when you call because of security reasons from Samsung. There are some reasons that why are Samsung phones that don't have record feature on ongoing calls & incoming calls on them.
Well, it's one of Samsung phones flaws. There's no built-in recorder on the device reason why there's no way to record a phone call. Video call may be visually recordes but not the audio. Samsung should take consideration of improvements. You may wanna install third party app to record phone calls.
