You can record a conversation or other audio using your iPhone’s built-in Voice Memos app. But if your iPhone isn’t handy, you can use your Apple Watch and turn to a free app called Voice Record Pro.
You can record audio directly through the app. Just press the record button. The app even displays a VU (Volume Unit) meter so you can monitor the volume of the audio. Press Stop when done. You can then play the recording from the Apple Watch app.
As another option, you can use the Apple Watch version as a remote to start and control an audio recording for the iPhone app. Whether you record from your watch or your phone, you can then use the iPhone version to edit the recording and save it or share it.