不定式短语是什么成分

Thesegreat royal events are unifying because they are “brilliant editions ofuniversal facts”, to borrow a phrase from Walter Bagehot, the great Victorianeditor of The Economist.

不定式短语为插入语，是说话人对引号内这部分的讲解。不定式的逻辑主语为说话人，即引号内部分是我说话人借用Walter Bagehot的原话。