The iPhone won't explode in the fridge, but it will damage it.
The iPhone uses lithium batteries. Lithium batteries are active in low temperature environments and will not explode. The low temperature will freeze the air inside the iPhone. There are chemicals in the air, moisture is trapped in the iPhone. When the iPhone is taken out of the refrigerator, the frozen moisture and temperature difference will cause moisture inside and outside the iPhone, damaging the motherboard. iPhone falls into water, the low temperature will cause the liquid in the screen to freeze, causing image distortion, fog will form in the camera, affecting the iPhone's ability to take photos, and low temperatures may cause the touch screen to become unresponsive or even unresponsive.