Final answer:
The phrase in question is a noun clause which serves as the subject of the sentence, embodying the idea of conspicuous consumption and the display of wealth through purchasing expensive items.
Step-by-step explanation:
The phrase 'Some people buy expensive cars simply because they can' is a noun clause.
A noun clause functions as a noun in a sentence and can often replace a subject or an object. In this case, the entire clause serves as the subject of the sentence, sharing information about what some people do.
It captures the concept of conspicuous consumption, where individuals flaunt their wealth by making purchases that are not necessarily practical but are intended to display their social status.