I-phone charger

If you mean a plug in wall charger, it is very likely dual voltage. So all you will need is a plug adapter so you can plug it in the socket, like this one https://store.ricksteves.com/shop/p/uk-power-adapter

It depends. If you use a plug with your charger, you will need an adaptor. If you just plug it into a USB port, you do not.

That said, many hotels now have USB ports for travelers to use, but I wouldn't count on it, so chances are you will need to bring a plug (or a power strip, like this one). And you will need an adaptor with that.

I was in Ireland in May and used this adapter with my iphone charger at all my hotels:

https://www.amazon.com/dp/B01MZD5T3E?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_3&th=1

Something like this is one piece and universal:
https://www.amazon.com/NEWVANGA-International-Universal-Worldwide-Charging/dp/B01FO4W5W2/ref=sr_1_3?crid=3DJC83L9NH6BQ&dib=eyJ2IjoiMSJ9.-zkc_-bjoO8zJD3SI4XHIKqa7_dkwW45HZ5NP_ma28bZ0zXaChcczmpa4S-JJULaNqfDJ5PH2mmcnx3f4qS-9HRq1VowDuN2pgpQS4z1hM-6QmhNct7L1JGn1BFRDZDykYoJkPuIDlotoSURNY2fH0y5jI41UraCB_2am9gm_xIMe4YGDywrj2kREOnIY9TwATbE13rFF5MopovQ5N_v8uWbsa822HVPAzB3nJZAX2puRKu5rFX0eVIHfpffMnc81ucBmsq6Ka0HWUHF0JU1oYP4QNiDptPDyGBqdOZH2DE.qnQRodzPCSdSEXTO5xM7t8HdLXzHaqoBgr8nYwl6WlM&dib_tag=se&keywords=universal%2Btravel%2Badapter&qid=1753480848&s=hi&sprefix=universal%2Ctools%2C167&sr=1-3&th=1