People who work in offices are frequently referred to as 'white-collar workers'.

这里的 be referred to as是个固定搭配吗？

be referred as不可以吗？ 

【答】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。

People who work in offices are frequently referred to as 'white-collar workers'.

【翻译】在办公室工作的人经常被称为“白领工人”。