Thanks for sharing this. I can download multiple videos with iFunia YouTube Downloader on my Mac, but don’t know can download the videos on iPhone too.
FYI, the iFunia works really well on downloading Youtube videos on Mac. Any would like to try it can visit its official page here: https://www.ifunia.com/video-converter-mac.html
Every time I transfer the video to iPhone manually, I would like to try this solution.