Not quite sure why you are bothering with the join, maybe because the OP tried to use it:

use warnings;
use strict;

my @num = qw(zero one two three four five six seven eight nine);

while (<DATA>) {
    s/([0-9])/$num[$1]/g;
    print
}

__DATA__
This is 1 great time 2 have a 3 way 4some.
When 5 and 6 together make 11.
Some 8 or 9 of us will see that.
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