During my working years I always had ready access to good recording equipment. This came in most handy when recording interviews by phone. Good telephone hybrids are expensive but make a big difference in quality.
Since retiring, I’ve used various tools for this task. I’ve mentioned Call Recorder for FaceTime which works well if both ends are using Mac gear. Years ago I tried Audio Hijack but found that glitchy. Probably a user issue.
Yesterday I tried a different setup. I made the call via Google Hangout and recorded the audio with ScreenFlow. I use ScreenFlow to record screencasts but found I could simply turn off the camera and capture the audio. I was pleasantly surprised with the result. ScreenFlow captured the audio in two channels so it was easy to tweak the audio for each. There might be better ways to skin this cat but this is the best combination of easy and quality that I’ve found.