Unir datos de 2 bases de datos diferentes

<?php

function connect($host = 'localhost', $dbname = 'voip', $user = 'homestead', $password = 'secret')
{
    try {
        $conn = new pdo("mysql:host=$host;dbname=$dbname",
            $user,
            $password,
            array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
        return $conn;
    } catch (PDOException $ex) {
        die(json_encode(array('outcome' => false, 'message' => 'Unable to connect')));
    }
}

$usuario = 'homestead';
$contraseña = 'secret';

$conn = connect('localhost', 'voip', $usuario, $contraseña);
$conn2 = connect('localhost', 'voip2', $usuario, $contraseña);

$sql1 = $conn->prepare("SELECT id, first_name, phone_number FROM bit_gxp_phonebook");
$sql1->execute();

$sql2 = $conn2->prepare("SELECT id, first_name, phone_number FROM bit_gxp_phonebook");
$sql2->execute();

$response1 = $sql1->fetchAll();
$response2 = $sql2->fetchAll();

$results = array_merge($response1, $response2);

$json_data = [];

for ($i = 0; $i < count($results); $i++) {
    $item = [
        'id' => $results[$i]['id'],
        'fist_name' => $results[$i]['first_name'],
        'phone_number' => $results[$i]['phone_number']
    ];

    $json_data[] = $item;
}

print_r(json_encode($json_data));