In fact, it's in the Measure app, which is one of the default apps that comes pre-installed on all Apple iPhones. So first, fire up the Measure app. You should see a camera viewfinder, which is used for measuring objects. Ignore that, and tap the Level tab in the bottom left of the screen.

Where do I find the level on my iPhone?

Open the Compass app. The first screen displays the typical compass for figuring out your direction, but a surprise lies ahead. Swipe the screen to the left and there you'll see the level feature.

Where is the level in iOS 14?

To find it, just open Measure, then tap the "Level" tab in the bottom right. Alternatively, you can long-press the Measure app icon and then select "Level" from the quick action menu.