You can use an multi-dimensional array with the json_encode function to achieve this structure.
$var = array(
    “contacts” => array (
        array(
            “id” => 1,
            “name” => “foo”
        ),
        array(
            “id” => 2,
            “name” => “bar”
        )
    )
);
echo json_encode($var);
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solved PHP generate json – list of categories [closed]