There are a few ways to make a Youtube banner on an iPhone. One way is to use the built-in banner editor in the iPhone app. Another way is to use a third-party banner editor such as BannerBuddy or Banner Maker. The first way is more difficult but can be done with some basic coding skills. The second way is more reliable and requires less coding. However, it may not be as user-friendly. Both methods require some creativity and effort, but they are both worth trying out if you want to create a Youtube banner on your iPhone.