I think you may try something similar to what I did a while ago (AFAIK I have it in Downloads Input classes File #9644, but I'm not sure).

I had a textbox for entering zipcode (phones in your case) and after I finished entering they got appended to the editbox like this

zip1
zip2
zip3

I also had some code to validate if the entry was already in the list and also I think I had an ability to highlight and delete entries.