use strict;
use warnings;

use Data::Dumper qw(Dumper);

my %people;

print exists $people{Foo} == 0;

print Dumper \%people;
if (exists $people{Foo}{phone}) {
    print "Good, Foo might have a phone\n";
} else {
    print "Foo has no phone\n";
}

print Dumper \%people;

print exists $people{Foo} == 1;