You can set the featured image size in second parameter based on this document
// without parameter -> Post Thumbnail (as set by theme using set_post_thumbnail_size())
get_the_post_thumbnail( $post_id );
get_the_post_thumbnail( $post_id, 'thumbnail' ); // Thumbnail (Note: different to Post Thumbnail)
get_the_post_thumbnail( $post_id, 'medium' ); // Medium resolution
get_the_post_thumbnail( $post_id, 'large' ); // Large resolution
get_the_post_thumbnail( $post_id, 'full' ); // Original resolution
get_the_post_thumbnail( $post_id, array( 100, 100) ); // Other resolutions
actually php cant check the responsive of screen. But if you want check the user run in mobile or not you can use this function.
if ( wp_is_mobile() ) {
echo get_the_post_thumbnail( $post_id, 'large' );
} else {
echo get_the_post_thumbnail( $post_id, 'thumbnail' );
}