To customize the “Add to Cart” button on mobile devices in WooCommerce, you can use a plugin such as WooCommerce Custom Add to Cart Button or SeedProd. These plugins allow you to change the “Add to Cart” button text, add a cart icon to the button, replace the text with just an icon, or change the background and text color.
Alternatively, you can create a custom “Add to Cart” button by editing the code of your theme.