You could return a tuple of (ERRMSG, VALUE). This makes it easy to return errors. It has the benefit of being very lightweight. Here's a script for testing:

#!/usr/bin/perl -w
use strict;
sub chk_phn {
   local ($_) = @_;
   return "missing input" unless defined $_;
   return "empty input" if $_ eq "";
   return "invalid character" if /[^-\d]/;
   s/-//g;
   return (undef, $_);
}
my ($err, $res) = chk_phn @ARGV;
$err = "UNDEF" unless defined $err;
$res = "UNDEF" unless defined $res;
print "<$err><$res>\n";
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