Dear stupid idiots,
Your firebomb 7 phones need never heat up to combustibility.
All you need do is add a thermal expanding plastic wafer to one of the power leads that is no more than 2x2mm. when it gets hot it expands and cuts power. This may be inconvenient for the user but it will never get hot.
The real expense for the re engineering would be an interim low power back up add on to fill in while the unit cooled.

I am incredibly stupid and I know how to fix your phones. Why didn't you?

clue: because you are stupid idiot.

btw the inventor of the thermal expanding plastic is a woman who made this plastic over a year ago.