I had a similar problem very recently with OVH. Though it's not related to smartphones.

I migrated my personal domain (nameserver and email) to a different IP address. After migrating the server, I wanted to change the glue record on OVH.ie. They detected some suspicious activity and prompted me to enter the code that was sent to my email, email on the domain that has unreachable namesevers because I couldn't log in to their dashboard. I had no 2FA enabled.

The interesting part about this is that I knew it might cause problems, so I also added a secondary email address to OVH, the one from our national academic research network. But OVH only sends codes to the primary mail! How useful ...