About charging Li-ion batteries in mobile devices
They are Lithium Ion, the company would be insane to not provide a decent safety. If the current or input voltage exceeds the packs max, nothing will happen because its regulated by the systems PMIC, which will output a charging voltage and current that is safe for use with the corresponding battery. Mobile phones are charged over USB which is a 5V 1 A system, it will never get near 9 or twelve volts, if it did the phone would get rather unhappy...  but this question is off topic. Its not a design question, go dig out a schematic for a phone and look at its power supply, and the charging circuitry. That will teach you more, but I am also sure you can find tons on google! 

the last question in your question. 

I race model touring cars, my packs come off the track hot, and get charged straight after, while still in most cases, hot, packs that aren't designed for this kind of use are likely to explode, so as long as the pack is used as its designed, it wont explode, a few things that could cause it to vent or explode. 

shorting. 

over charging. 

under charging. 

drawing to much, or using a undersized battery for your intended application. 

puncturing the cell. 

Dodgy electronics.