"Phone already exists" when setting up TFA for multiple email addresses

"Phone already exists" when setting up TFA for multiple email addresses

I've had to switch on TFA for all my email addresses, some of which I use for different tasks such as info and accounts as well as having a personal email address.  Now having set it up for two addresses the TFA system won't accept my mobile number to set it up for other addresses, which is stupid, and of course now it is switched on the other email addresses have stopped working on my devices! Why are you expected to have multiple mobile phone numbers just to set up your email addresses?

Has anyone else had this problem and got a work around?

Thanks in advance, 

Yours

Frustrated!