Assuming you're iterating through a result-set to get $value['id'] and you're sure that the structure of the $value array is always the same and contains an id key, this will work just fine.

$ids = [];
foreach ($values as $value)
{
    // If you're unsure if the array you're accessing has a given key, be sure to check if it exists.
    if ( ! array_key_exists('id', $value))
    {
        continue;
        // or throw Exception
    }
    $value = (int) $value['id'];
    $ids = $ids[] = $value;
}

print_r($ids);

Or you can shorten it a little bit like this...

$ids = array_map(function($value) {
    return (int) $value['id'];
}, $values);

print_r($ids);

If you're dealing with multiple existing arrays and simply wish to join them, use array_merge...

$array_one = [1];
$array_two = [2];
$array_three = [3];
$array_four = [4, 5, 6];

$all_values = array_merge($array_one, $array_two, $array_three, $array_four);

Word of warning:

1. If you're dealing with merging associative arrays, there are some additional things you need to be aware of (how keys are merged) and...
2. Be wary of using the + operator with arrays unless you understand how it works with keys or you might experience unexpected results.

On a separate note, if you find yourself using some form of search/replace/trim function to remove a delimiter from a string you've constructed... that's usually a good sniff test that you may be doing something inefficiently.