chomp (my $name = <STDIN>);

if ($name =~ /^derrick\b/i)
{
    print $phnums{"derrick"};
}
elsif ($name =~ /^juan\b/i) {
         print $phnums{"juan"};
} 
elsif ($name =~ /^kevin\b/i) {
        print $phnums{"kevin"};
    }
[download]

Also you sould Read The Frienly Manuals more often :) Update:

chomp(my $name = <STDIN>);
$name =~ /^$_/ and print ($phnums{$_}.chr 10) for keys %phnums
[download]