Although you may be best following ikegami's advice and altering your structure, you can in fact get it to output exactly as you want from your existing structure with:

 
my $xml_obj = XML::Simple->new( Keeproot => 1,
                                GroupTags => {phonenumbers => phonenum
+ber},
                                KeyAttr => [-name] );
[download]

Which may or may not be uglier than you expected.

/J\