If you want to download your favorite YouTube videos to your iPhone, you will need an app such as Titan Player. This app has a free version or a paid version and is available on the iTunes App Store. After you have downloaded the app, open it and click on the browser button on the bottom of the screen to navigate to YouTube. You do not have to agree to download the official YouTube app though, so you can just close that popup if it appears.
When you have found the YouTube you want to download to your iPhone, play it and then select “Cache Video to Memory”. This will prompt the video to download to your iPhone. When it’s finished loading, hold down on the “Videos” icon on the bottom of the screen, hold the video you just downloaded and choose the option to “Save to Camera Roll.”
Keep in mind that YouTube videos take up a lot of space, so if you notice that you are using too much space and want to clear some out, delete some of the YouTube videos that you no longer want to save.