Capture audio from videos

I want to listen to videos on my Iphone. I don't want to download the video but just create an mp3 so I can listen to the audio on my phone. I have about 19 videos to capture the audio. I will have about 10-20 every month in my study program.

Here is the play list. they are all about 30-45 minutes long and there are 19.
https://www.youtube.com/playlist?list=PLxtDdds6EoqVut7DTobtRdyibQivL0jE7

I have no idea how long this will take, but should not take longer than the videos, I want good quality and good volume control.