Narrative:

While at cruise altitude I was using the calculator on my phone to determine fuel burn to the next waypoint. I was the non-flying pilot and ATC gave us a change of frequency. I placed the phone on my right leg and reached forward to change the frequency. The phone fell from my leg and onto the floor. I heard the phone hit the floor. I left it there and changed frequencies and checked in with ATC. I went to pick up my phone and while I was doing this the aircraft alerted us to the cabin pressure altitude climbing. I noticed we were depressurizing and so we performed our memory items and requested priority handling and initiated a descent. At this point the passenger oxygen masks were activated. As we were descending I realized the dump button was pressed and surmised that when the phone fell it must have hit the guarded dump switch; bent the guard causing the dump button to engage and begin depressurizing the cabin. When we leveled at 10;000 feet we continued the checklist. We were right over ZZZ airport so this is where we diverted to. Because we were overweight and the first officer was new I took control of the aircraft and made a smooth landing with approximately 300 ft/min descent rate. We landed without further incident. Passengers reported they were fine and did not want medical attention.in retrospect I would put any equipment that I have in my hands down in the proper place prior to doing anything else in the cockpit.

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Original NASA ASRS Text

Title: EMB-145 flight crew reported Captains cell phone fell from his leg and hit the pressure dump switch; causing cabin depressurization.

Narrative: While at cruise altitude I was using the calculator on my phone to determine fuel burn to the next waypoint. I was the non-flying pilot and ATC gave us a change of frequency. I placed the phone on my right leg and reached forward to change the frequency. The phone fell from my leg and onto the floor. I heard the phone hit the floor. I left it there and changed frequencies and checked in with ATC. I went to pick up my phone and while I was doing this the aircraft alerted us to the cabin pressure altitude climbing. I noticed we were depressurizing and so we performed our memory items and requested priority handling and initiated a descent. At this point the passenger oxygen masks were activated. As we were descending I realized the dump button was pressed and surmised that when the phone fell it must have hit the guarded dump switch; bent the guard causing the dump button to engage and begin depressurizing the cabin. When we leveled at 10;000 feet we continued the checklist. We were right over ZZZ airport so this is where we diverted to. Because we were overweight and the First Officer was new I took control of the aircraft and made a smooth landing with approximately 300 ft/min descent rate. We landed without further incident. Passengers reported they were fine and did not want medical attention.In retrospect I would put any equipment that I have in my hands down in the proper place prior to doing anything else in the cockpit.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.