pear install -a Services_Yahoo_JP_Furigana-alpha

<?php
require_once 'Services/Yahoo/JP/Furigana.php';

$app_id = '';

try {
    $yahoo = Services_Yahoo_JP_Furigana::factory('furigana');
    $yahoo->withAppID($app_id);
    $yahoo->setSentence('既存の設定で極小になっている');
    $yahoo->setGrade(1);
    $result = $yahoo->submit();

    $str = null;
    foreach ($result as $word) {
        $str .= isset($word['Furigana']) ? $word['Furigana'] : $word['Surface'];
    }
    echo $str . PHP_EOL;
} catch (Services_Yahoo_Exception $e) {
    die($e->getMessage());
}