Answer
The camera lens moves farther away from the sensor.
Work Step by Step
Moving closer to the subject decreases the object distance. The focal length of the lens stays constant.
Equation 23-8, $\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}$, tells us that if $ d_{o}$ decreases and f stays the same, the image distance $d_{i}$ must increase.