How do browsers calculate the resolution of the phone?

If you go to any phone specifications on any website they usually have resolutions like:

• 1080 x 2340 pixels, 19.5:9 ratio (~409 ppi density)

• 720 x 1280 pixels, 16:9 ratio (~294 ppi density)

But using the same phones and going to a website that uses max-width of 600px, the media query still works. Also when checking the resolution on whatismyresolution it says that the width is 360px and the height is around 700px on both phones. How is the resolution calculated on the browser?