refer
refer to sb. as... 是固定词组，意为“称某人为...；把某人称作...”，介词to不可省略。句子用了其被动式be referred to as （某人被称作），等于be called.
又如
Her Chinese friends referred to the Empress as their venerable ancestor.
她的中国朋友们说这位女皇是他们值得敬仰的祖先。
English is referred to as a universal language.
英文被称为世界语言。
Coal is usually referred to as a fossil fuel.
煤通常被称为矿物燃料。