The below information gets somewhat technical, so here's the quick summary: If the charger (which is actually just a simple power adapter) is not a piece of junk, the phone will not be damaged by it.
First of all, the charging is controlled by the phone and circuitry inside the battery to ensure safe operation. Lithium Ion batteries can become very dangerous if not charged properly.
The thing you plug into the wall is just a power adapter that turns AC into 5V DC and puts it over a USB interface. It has little to no intelligence, other than possibly some safety features and circuitry to decrease power consumption.
If you hear of a micro USB "charger" frying the phone, then it was putting out the wrong voltage. This is most likely to happen with the cheap $5 unbranded "chargers", such as some found online.
If you have a power adapter that came with any other phone, or a reputable retailer that wasn't extremely cheap, it should be high quality and will be very unlikely to fry the phone unless it has been damaged or is simply defective.
If the voltage from the power adapter is wrong (too low or too high): This can potentially damage the phone and/or battery
Regarding the current (mA) rating:
- Too low - phone will charge slowly or not at all
- Too high - phone should only draw what it needs. No damage will occur if everything is designed properly. Charging current decreases as the battery charge level increases, so no power adapter runs for its specified maximum current levels for the entire duration of the charging process.
As stated earlier, the OEM adapter is rated at 1,000mA (1A) 5VDC. The spec for USB is 5V, and the standard current is 500mA. If you plug your phone into your computer to charge, it is most likely getting no more than 500mA. That's why it charges slowly from a PC.