The phone itself accepts standards USB voltages that are the same around the world. The power supply you plug into the wall needs to accept various voltages and frequencies depending on its intended retail location, and should have a label on it listing the voltage and frequency ranges (if it didn't get worn away by use, as often happens). I found this site, which has a good write up on Ireland's electrical outlets.
https://www.power-plugs-sockets.com/ireland/
If you're in a country that needs an adaptor and/or converter to travel to Ireland, I think I'd just save the hassle and buy a new power supply there. It'll still output the same USB standard power ratings and not be as cumbersome as using additional adapters. If you plan to also power other devices (laptop, camera chargers, appliances you bring, etc), then buying an adaptor and converter may be a worthwhile investment. USB power supplies are generally cheap, so that may even be cheaper than the adaptors.