Light the fuse and keep passing the phone.
Holding it when it blows? Penalty.
Hot Potato Bomb is a game where you keep passing a bomb that could go off at any moment, and whoever is holding it when it explodes gets the penalty. The phone is the bomb, and the rules take ten seconds to explain, so you can start right away at any party.
The fun is all in how long you hold it. Someone tosses it on the instant they get it, someone plays it cool and gets blown up, someone shoves it at the next person, and the laughs come naturally.
If just passing it gets boring, try mission mode. Every time you get the phone, a mission like "An animal starting with S", "Clap three times" pops up, and you have to read it out loud and answer it before you pass. There are 46 missions, and the same one never comes up twice in a row.
The app doesn’t judge the answer. Someone yelling "That doesn’t count!" is part of the game. To stop accidental taps right after you get the phone, the pass button is locked for 1 second after a mission appears.
If the settings showed the exact seconds, people could watch the timer and figure out "it’s about to blow". Then nobody is nervous at the start and only the last person gets unlucky. So fuse lengths are only described as "about one lap / two or three laps / goes for a while". The elapsed time is shown on screen, but the deadline never is.