We bought these for our USB chargers last year for use in Italy, and I’m using one right now in Spain.
All decent USB chargers and decent phones (iPhone, Samsung, etc) are multi-voltage so all you need is the plug adapter. If you have doubts, you can give yourself some peace of mind by reading the super-fine print that everybody ignores on your usb charger (or looking at the online description) where you should see something like “input: 100-240v” printed.
https://www.amazon.com/gp/product/B097GCZWMM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
Above advice is for electronics only. As others have said, for mechanical stuff like hairdryers you’ll need an actual converter.