register_block_type( 'some/block', array(
    'render_callback' => 'render_my_block',
    'attributes' => array(
        'stuff' => array(

        )
    )
));

function render_my_block( $attributes ) {
  // $attributes['stuff']
  return '<h1>Hello frontend</h1>';
}

registerBlockType( 'some/block', {

    title: 'Some block',

    attributes: {
        stuff : {

        }
    },

    edit( { className, attributes, setAttributes } ) {
        return (
            <Fragment>
                <SomeInput />
                <SomeOtherInput />
                <Preview>
                    // I need to get contents of PHP function render_my_block here,
                   // based on current attributes.stuff
                </Preview>
            </Fragment>
        );
    },

    save( { attributes } ) {
        return null; // server side
    }

} );