On this page of our guide to BioShock Infinite you will find the third part of a detailed walkthrough of Chapter 32 - Comstock House. This is a very short section, which you have to follow towards the director's office. Also, you will find a new voxophone.
Shortly after defeating the Boy of Silence (a new variety of boss), the primary objective of the mission will change. As a result, you must wait until the elevator from the picture above comes down to the gate.
Enter the elevator, pick up Voxophone #70 and travel to the upper floor. You will advance to the next chapter of the campaign.