How to Record Calls on iPhone

Here is another way involving a Mac and EarPods. Attach EarPods to the Mac. Then attach the remote controller of the EarPods (which contains a microphone) to the iPhone. The microphone should be attached near the speaker. To fix it on the phone you can use a tape or a bulldog clip. Or just clamp it under the cover:

Use QuickTime to create a sound file. Click File > New Audio Recording. Since you attached your headphones to the Mac, the External microphone will be selected by default.

Then hit the red button to start the recording. Make a call. The described technique doesn't require speaker mode and gives a good sound quality without noises. Your mouth is farther from the EarPods micro than the speaker of the iPhone. The distance compensates the differences in the sound volume, thus the both voices in the call will have similar loudness.