IPhone plugged in All the time a fire hazard?

I have an old iPhone 4, the screen is shattered (a lot) and some of the glass fell off lol. Anyway the phone itself still works. I plan on using the phone as an airplay server (jailbroken), and this would involve keeping it plugged in and effectively 'charging' 24/7.Is this a fire hazard? For what it's worth I would be using a brand new charging cable (genuine - from apple).

Should I be worried? Is this a disaster waiting to happen?

ALSO, as an alternative, do you think it would be smarter to keep it plugged in all the time and have it charge itself every 12 hours with one of those outlet timers (similar to the christmas light timers)? This way it would only be plugged in for 12 hours of the day.

I'm not a fire genius or anything, but I'm pretty sure it would be fine. I keep my phone plugged in anytime I'm home and I've never had an issue. If the phone becomes hot or anything though, I would unplug it.