Imo this is one of those things best left unhandled, eg. "just use a plain mostly unvalidated textfield, and throw and error only when you want to use that data via another system like for a text message campaign". Mostly in real-life if you want to target the entire freaking planet (not just 99% of phone using people, but 99.999%), you'll get to realize that any validation is not enough and that some phone numbers need to contain arbitrary letters and symbols in them (better don't ask... the world is big and weird :P), and that yeah, those numbers will not be procesable by things like Twillio, but human users with local knowledge will know how to actually "dial" them...
But it needs to be a conscious decision, to consciously choose to not-validate and to understand that you give up the ability to 100% target phone numbers for things like 2-factor-auth later on.
Not "forget that phone numbers need to be validated" and then, go and say, "oh, let's do phone-based 2-fa mandatory" or whatever user interaction messup like that.
Imo this is one of those things best left unhandled, eg. "just use a plain mostly unvalidated textfield, and throw and error only when you want to use that data via another system like for a text message campaign". Mostly in real-life if you want to target the entire freaking planet (not just 99% of phone using people, but 99.999%), you'll get to realize that any validation is not enough and that some phone numbers need to contain arbitrary letters and symbols in them (better don't ask... the world is big and weird :P), and that yeah, those numbers will not be procesable by things like Twillio, but human users with local knowledge will know how to actually "dial" them...
But it needs to be a conscious decision, to consciously choose to not-validate and to understand that you give up the ability to 100% target phone numbers for things like 2-factor-auth later on.
Not "forget that phone numbers need to be validated" and then, go and say, "oh, let's do phone-based 2-fa mandatory" or whatever user interaction messup like that.