In the given sentence, "I am afraid you cannot use this telephone; it is out of order," the phrase "out of order" is an idiomatic expression used to indicate that something is not functioning properly or is temporarily unavailable for use.

When a device or machine is "out of order," it means it's not working correctly, and using it would be futile.

In this context, the sentence conveys that the telephone is dysfunctional or experiencing some technical issues, making it impossible to use at that moment.