Basically, the air pressure inside the cabin is higher than it is outside of the plane to enable the people onboard to breathe normally. That's why, if a window happens to break, the air inside would escape at high speeds, taking small objects like phones or magazines (or sometimes larger things, like people) with it.

If a plane window were to break at a high cruising altitude (typically above 30,000 feet), it would trigger a rapid cabin decompression. Because the air pressure inside the plane is much higher than the thin air outside, a powerful "explosive" rush of air would exit through the opening, potentially pulling unsecured objects or even a nearby passenger toward the hole. Inside the cabin, the temperature would instantly plunge to as low as -50°C, and a thick mist or fog would likely form as the moisture in the cabin air condenses. Oxygen levels would drop dangerously low, causing "hypoxia" (oxygen deprivation), which is why the yellow oxygen masks drop from the ceiling immediately. Passengers have only about 15 to 30 seconds of "useful consciousness" to put their masks on. The pilots would immediately initiate an emergency descent to around 10,000 feet, where the air is thick enough for people to breathe without masks. While modern multi-layered windows make a total failure extremely rare, these protocols ensure the plane can land safely.