I'm assuming you are selecting from the official backgrounds that are under Settings > Wallpaper > Choose a New Wallpaper menu. Where do i find the wallpaper settings on my iphone?
2 You can also turn on Dark Appearance so that your iPhone dims your wallpaper depending on your ambient light. How to Change the Background on My iPhone 1 Go to Settings, tap Wallpaper, then tap Choose a New Wallpaper.