How should the final telephone call affect the audience?

Birling is making another sweeping generalization about “the famous younger generation who ... can’t even take a joke” when the phone rings. Birling answers it, listens, and puts the phone down. Looking at the others, panic-stricken, he utters the play’s final lines:

“That was the police. A girl has just died—on her way to the Infirmary—after swallowing some disinfectant. And a police inspector is on his way here—to ask some—questions—”

With that, the curtain falls.

This underscores Priestley’s warning about responsibility. The phone call reinforces the inspector's message with the remaining party members who feel they have escaped the punishment for their sins.