After watching a young relative type on an iPhone recently, I realized he didn't know how to use the "iPhone caps lock" feature. I assumed a person younger than me would know how to use the iPhone caps lock feature, lol, but it's not too surprising, because enabling the caps lock feature isn't the most obvious thing in the world.
iPhone caps lock
To use the iPhone caps lock feature, whenever you're typing something -- like composing an email -- just tap the iPhone Shift button twice. You need to do this quickly, similar to a double-click.
When you do this successfully, you'll see the Shift button background turn blue, and the up-arrow turn white. (As a point of comparison, the "normal" shift key displays as a bold, white up-arrow on a gray background, and the lowercase mode is shown as a gray button with an outlined white up-arrow.)
After you've enabled the iPhone caps lock functionality this way, just tap the Shift key again when you want to return to the "normal" lowercase mode.