First is traveling quite a bit with poor cell signal. This one is unfortunate especially with banks that have no alternative 2fa other than a phone based OTP.
Why phone? I would believe it's the one thing that near ubiquitous that has a very low barrier to entry. I never had to train my mother how to use OTP when it's an SMS. If she was required to use google authenticator, I'd probably get a phone call every time she had to login.
As for "phone numbers are a horrible identifier" I would say it is "secure enough" for many scenarios.
Typically 2fa systems require a bad actor to have both a password and a physical device.
To be pedantic, the OTP is not considered an identifier, but a password that requires a physical device.
The barrier of a bad actor having both my PW and my device (as a PW) is supposed to raise it high enough that it's unrealistic. Obviously this doesn't work 100% of the time, because phishing and social engineering.
So, sure my device can change hands, but it is unlikely to have changed hands AND that same person has my password AND they are a bad actor.
I live overseas (US expat). To get around many OTPs from US based services I use: https://anveo.com/. Google Voice cannot do shortcode SMS for places like Bank of America. The website looks like it was built in 1995, but it's effective.