I think all of my breakups have been done by phone, whether I was the one initiating the break-up or not.
I had not heard of any rule of etiquette requiring a face-to-face meeting.
It is also true that people in some sort of relationship (using the term in its broadest sense) call each other on the phone, discuss things, make requests or demands, state positions, etc. Often, all it takes is saying "no" to one of these requests/demands/whatever from the other person to break up the relationship.
So I think a rule not to break up by phone is just unworkable, unless you have a more general rule to never discuss anything important by phone.
I do think that breaking up by an e-mail message is very tacky and insensitive. But, on the other hand, what are you going to do about it? If the other person in the relationship does not want to see you anymore, they don't want to see you anymore. Period. End of story. If that includes not wanting to see you for a "final" conversation, so be it.