David, I'm assuming you mean a smart phone. I've always had good luck with Moto Android smart phones. You can find a very basic one for about $100 to $150. You want an "unlocked" phone so you can use it with any mobile company. You can buy Moto phones on Amazon. If you want to get your feet wet, buy an older "renewed" phone like the Moto G7 for about $100. It comes with a short warranty but basically a used phone that has been refurbished. Maybe once you get the hang of a smart phone, you can spend more money on one you like better.
Phones use SIM cards to connect to a service provider to have actual phone service. You insert the physical SIM card from say T-Mobile or AT&T into the phone and then you pay for monthly service...or get a prepaid plan for limited use. In Ireland, you can buy an Irish SIM card that will work locally, once you get there.
But...you can use any smart phone on WiFi, which is internet service tied to a location like a hotel or restaurant, without having a SIM card or any paid mobile service. If you have WiFi at home, that's all you need to buy and use a smart phone at home. It won't work once you move too far from your WiFi - that's where you would need a SIM card for actual mobile service. If your trip isn't for a few months, buy the cheap smart phone now, start playing with it at home, get used to it. You can even buy cheap prepaid service with Tello (uses the T-Mobile network, so they need to have decent reception where you live at home, and T-Mobile doesn't always offer good reception in some rural areas) for about $10/month if you want some cheap mobile service to play with at home, away from WiFi. But Tello won't work in Ireland. It's just something to get you started without spending a bundle.
