Generally phones latch on to the best network they can find, but to use it most phone companies(your provider) want you to have authorised use abroad at some point.
If you have an on-line account you should be able to see it.
One of the many Brexit benefits for UK citizens, mobile phone companies can and do charge extortionate roaming charges for the use of your phone while in mainland Europe.
If we want to use this as another anti Brexit rant fine but I'm with vodafone on contract and don't pay any more to make calls in Europe than I do at home. It's not the only provider who don't hike up their roaming charges either.
Smurf my phone has always found its own network as soon as I've arrived - Vodafone ES for me in Spain. The cheapest way to make calls though is to use a local free wifi (hotel, villa etc) and use Whatsapp.
"From the start of 2023, new sign-ups and upgrade customers will lose this benefit; existing customers will continue to enjoy this perk provided they don't change their device or move to a sim-only contract. The roaming charges will be 10p a MB of data, 20p a text and 55p a minute for calls." 2 Jul 2022