use strict;
use warnings;

use List::Util q{first};
use Data::Dumper;

open my $inFH, q{<}, \ <<EOD or die qq{open: $!\n};
 1:gash line
 2:phrase4
 3:akjdakj
 4:fwefkwe
 5:phrase5
 6:phrase1
 7:adsfwfw
 8:phrase3
 9:phrase5
10:jkjd wsekjw wiu
11:phrase2
12:wewefwefwf
13:another line
14:dsjwjk
15:adsfwfw
16:phrase3
17:another line
18:adsfwfw
19:phrase5
20:phrase6
21:ertgerher
EOD

my @lines = <$inFH>;
close $inFH or die qq{close: $!\n};

my @phrases = map { qq{phrase$_} } 1 .. 6;
my $cumulativeOffset = 0;
foreach my $phrase ( @phrases )
{
    my $rxPhrase = qr{$phrase};
    my $lineNo =
      first { $lines[ $_ ] =~ $rxPhrase } 0 .. $#lines;

    unless ( defined $lineNo )
    {
        print qq{$phrase: not found in sequence\n};
        next;
    }

    $lineNo ++;
    $cumulativeOffset += $lineNo;

    print qq{$phrase: $cumulativeOffset\n};
    splice @lines, 0, $lineNo;
}

##</code><code>##

phrase1: 6
phrase2: 11
phrase3: 16
phrase4: not found in sequence
phrase5: 19
phrase6: 20