Hi @markd,
Thanks for your reply.
I have just collaborated with my colleagues on this one and it looks like the Send Phone Message action happens after the user has inputted their phone numbers. Unfortunately, there isn’t a way to have a drop-down for the available country codes for SMS MFA enrollment.
In this situation, I recommend creating a feedback request asking for this feature.
I hope this helps!
Please let me know if you have any questions.
Thanks,
Rueben