You can download the iOS 14 and iPadOS 14 wallpapers, in their full resolution, below. Be sure to click through and save the full resolution wallpaper, then set it via the Photos app or Settings app on your iPhone.
Apple usually releases a completely new set of wallpapers in conjunction with new hardware, so expect the iPhone 12 update this fall to bring even more choices to the wallpaper selection in iPadOS 14.