The phrase in this sentence that is an <u>adverbial phrase</u> is: <em>"For we are cut off from all the rest of the world."</em>
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 <em>How? Where? Why?</em> or <em>When?</em>
In this particular example, the speaker says: "<em>We are cut off from all the rest of the world</em>", so this adverbial phrase answers to the question: How are we cut off? The response being: "<em>We are cut off from all the rest of the world</em>".