In 2.0:
../*[name()=tokenize($contactlist, ',')]
There's no tokenize() in 1.0, though there are equivalent extensions in some products. The best thing is to preconvert "phone,ext" into <list><kw>phone</kw><kw>ext</kw></list> and then you can write
../*[name()=$list/kw]
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference