I have an iPhone as my main phone but travel with a Pixel as well. When in the EU I put my German SIM in the Pixel and buy a EU data plan and it becomes my primary phone. The iPhone stays in a zippered cargo pocket -- it is mainly so people in the US can reach me and if I need to contact somebody back in the US. As I am mostly retired these days, I don't need to do that so much.

Many years ago I had an iPhone that wouldn't charge and it was nice to have another phone that I could use. The one trip I didn't bring a backup (it was a bicycle tour and I was managing weight) I managed to drop my phone on a cobblestone street and broke the screen. Ended up buying an overpriced (for what it had) Samsung to use as a replacement.