Choose the right resolution for a camera photo wallpaper
A phone wallpaper looks best when the shape of the image matches the screen. Reading the aspect ratio tells you that shape.
Aspect ratio is the relationship between width and height. A photo straight from a camera might be 4:3, while many modern phone screens are close to 9:19.5 or 9:20. When those two shapes do not match, part of the photo is cropped or the image is stretched.
There is no single resolution that suits every phone. Screens differ in size and pixel density, so work from your own phone's screen.
Find the screen size of your phone in its display settings or in the manufacturer's specification. If your screen is 1080 pixels wide and 2400 pixels high, a wallpaper of about that size or slightly larger is a good target. Open the Aspect-ratio calculator and enter the pixel size of your photo and your screen. It reports the simplified ratio and a matching height for a chosen width. Open the Wallpaper cropper and enter a width and height that match your screen. Move the horizontal and vertical position until the subject sits where you want it, then create the image. Download the result and set it as your wallpaper in your phone's display settings.
You can also browse ready-made wallpapers that are already sized for phones.