The Parallax theme will slightly crop the various home page banner images on both desktop and mobile with the 'Crop parallax mobile banner images' setting. This typically allows for a greater display area on mobile instead of a very narrow banner, which can better display the banner text:
If you would prefer to display the entire banner images on mobile without any cropping/zooming, you can disable this setting through the theme editor. Head into Customize > Select your Banner image section > scroll down to Theme Settings > uncheck 'Crop parallax mobile banner images':
