Which phrase in this sentence is an adverbial phrase?

But, you see, the Land of Oz has never been civilized, for we are cut off from all the rest of the world

The phrase in this sentence that is an adverbial phrase is: "For we are cut off from all the rest of the world."

Explanation:

Let's remember that an adverbal phrase is a group of two or more words that function as an adverb in a sentence. This adverbal phrase can describe a verb, an adeverb, or an adjetive. They usually answer questions such as How? Where? Why? or When?

In this particular example, the speaker says: "We are cut off from all the rest of the world", so this adverbial phrase answers to the question: How are we cut off? The response being: "We are cut off from all the rest of the world".

The phrase for we are cut off from all the rest of the world