replace

$a="ajdkhhkd-1";
$b="ajdkhhkd-2";
$c="ajdkhhkd-3";
$d="ajdkhhkd-4";
$e="ajdkhhkd-5";

$arr = array($a,$b,$c,$d,$e);

$log = '';
foreach ($arr as $texto) {
    $log = $log . $texto."<br>";
}

$modelo = file_get_contents('api.html');
$modelo = str_replace('{LOG}', $log, $modelo);
$modelo = str_replace('{TITULO}', 'Teste de modelo', $modelo);

echo $modelo;