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':
When "Crop parallax mobile banner images" is not enabled, the height of the banner image is defined by the image's height. This will ensure the image is not cropped, and if the amount of text exceeds the height of the image, the text will be cropped.
When "Crop parallax mobile banner images" is enabled, the height of the banner is defined by the text. The more text inside of the banner, the larger the image becomes center-cropped.