A lot of such chargers will work with a wide array of voltages and frequencies. It's not uncommon for chargers to be specified as 100-240 VAC 50-60 Hz, which will work essentially anywhere in the world (where there is a public power grid) with simply a physical adapter for the plug.
@HaLaBi is right that in the case of a cell phone charger it probably doesn't matter, but if you want to be certain, the only real answer is to look at the charger itself and see what it says. If it says (for example) 100-240 VAC 50 Hz, it might work but it also might not work. If it says 200-240 VAC 50-60 Hz, you'll be fine. And so on. Note that VAC may alternatively be written V~.