If you’ve dropped your phone onboard a plane, it’s advisable to ask the cabin crew for assistance. Don’t try to pick it up yourself — Especially if it is under the seat.
Airlines are encouraging passengers to ask representatives to retrieve dropped phones for them because they often fall into the seat’s mechanism. On more than one occasion, customers moved their seats to retrieve their phones, and ended up crushing them with the same mechanism. That caused them to smoulder and damage the seats, which is a fire hazard.
Living in the age of exploding smartphones, we can’t really handle them in quite the same way that we used to. The consequences of dropping or running them over are greater than ever (exploding batteries, cracked screens, etc).
Lithium, one of the ingredients powering our lithium-ion batteries is a highly reactive element. Both a lithium-ion battery’s explosion hazard and its power/compact nature can be attributed to lithium’s reactivity.
This also means that you don’t want to expose the innards of a lithium-ion battery to air or water, as that can cause a dangerous reaction as well. This is seldom an issue, as most people don’t go out of their way to burst these things open (or run over them), but it’s good to know if you ever do want to.