I take a slightly different approach because I have to deal with foreign phone numbers also. This sub seems to work pretty good for me. If it can't find a format it just splits it up into groups of threes and sends it back.
HTH

sub fphone {
    shift;
    s/[\s|\n|\r]//g;    # strip space and newlines
    s/[-|)|(|.]//g;     # strip seperating chars
    s/(x|ex|ext\.)(.*)$//;      # Extension
    my $ext = $2;       # save extension
    my $n = '';
    my $l = length($_);
    if (($l == 12)||($l == 13)) {
        m/(\+\d{2}|\d{3})(\d{3})(\d{3})(\d{3})/;
        $n .= "$1 $2 $3 $4";
    } elsif (length == 11) {                # us with leading 1
        s/[+]//g;
        m/(\D)?(\d{3})(\d{3})(\d{4})/;
        $n .= "$1 " if $1 =~ /\d/;
        $n .= "($2) $3-$4";
    } elsif ($l == 10) {                    # us regular
        s/[+]//g;
        m/(\d{3})(\d{3})(\d{4})/;
        $n .= "($1) $2-$3";
    } else {
        s/(\d\d\d)/$1 /g;
        $n .= $_;
    }
    $n .= " Ext. $ext" if $ext;
    return $n;
}
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