Update: Mine gives combinations, not "phrases", so may not be a wanted solution. Thanks, ikegami.

Using Math::Combinatorics:

use warnings;
use strict;

use Math::Combinatorics;
use Data::Dumper;

my $phrase = 'camel perl book';
my @data = split /\s/, $phrase;

my @sets;
foreach my $count (1..@data) {
    my $combinat = Math::Combinatorics->new(
        count => $count,
        data  => [@data]
    );

    while(my @combo = $combinat->next_combination()) {
        push @sets, join ' ', @combo;
    }
}

print Dumper \@sets;
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