Replace content in between tags for data from another php file

Ok whole case, updated, I have some code saved and encoded in the database like this:

W1BIUF0KW1ZJRVdJRF0xWy9WSUVXSURdCjw/ICRjb25uID0gbmV3IFBETyggREJfRFNOLCBEQl9VU0VSTkFNRSwgREJfUEFTU1dPUkQgKTsgJHNxbCA9ICJzZWxlY3QgKiBmcm9tIHV6aXZhdGVsZSI7JHN0ID0gJGNvbm4tPnByZXBhcmUoICRzcWwgKTskc3QtPmV4ZWN1dGUoKTskY29ubiA9IG51bGw7IGZvcmVhY2ggKCAkc3QgYXMgJHN0cmVzdWx0ICkgeyA/Pgo8PyBlY2hvICRzdHJlc3VsdFsiaWQiXTs/Pgo8PyB9ID8+ClsvUEhQXQoKCgoKCgoKCgoKCgoKCgo=

decoded result is this:

[PHP]
[VIEWID]1[/VIEWID]
<? $conn = new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD ); $sql = "select * from uzivatele";$st = $conn->prepare( $sql );$st->execute();$conn = null; foreach ( $st as $stresult ) { ?>
<? echo $stresult["id"];?>
<? } ?>
[/PHP]

Then I have root file where I download all template parts that are encoded like I stated, I decode them, take the code inside [PHP][/PHP] and create a seperate phpview file that generates some content and that content I need to be swapped for the previous code that was inside [PHP][/PHP]. Of course If I generate from that php file another html file I can use file_get_contents, but I would like to find approach with just the one php file

<?
if ( !defined( 'DB_DSN' ) ) {require( "./../../pripojeni.php" );}
$conn = new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD );


function get_string_between( $string, $start, $end ) {
  $string = ' ' . $string;
  $ini = strpos( $string, $start );
  if ( $ini == 0 ) return '';
  $ini += strlen( $start );
  $len = strpos( $string, $end, $ini ) - $ini;
  return substr( $string, $ini, $len );
}

function replace_between($str, $needle_start, $needle_end, $replacement) {
    $pos = strpos($str, $needle_start);
    $start = $pos === false ? 0 : $pos + strlen($needle_start);

    $pos = strpos($str, $needle_end, $start);
    $end = $pos === false ? strlen($str) : $pos;

    return substr_replace($str, $replacement, $start, $end - $start);
}

$aktivniverzeproaktivniobsah = $_GET[ "id" ];
$sqlaktivniobsah = "select tp.* from template tp left join sekce sk on sk.template=tp.id left join verze vz on vz.id=sk.kverzi where vz.id=$aktivniverzeproaktivniobsah order by sk.poradi ASC";
$staktivniobsah = $conn->prepare( $sqlaktivniobsah );
$staktivniobsah->execute();
$conn = null;
$contentdecoded="";

foreach ( $staktivniobsah as $aktivniobsah ) {
  $idcko = $aktivniobsah[ 'id' ];
  $contentdecoded .= base64_decode( $aktivniobsah[ "obsah" ] );
}

if ( str_contains( $contentdecoded, '[PHP]' ) ) {
  $str = get_string_between( $contentdecoded, '[PHP]', '[/PHP]' );
  $idview = get_string_between( $contentdecoded, '[VIEWID]', '[/VIEWID]' );
  if ( !empty( $idview )and!empty( $str ) ) {
    $fp = fopen( 'wms/admin/views/view' . $idview . '.php', 'w' );
    fwrite( $fp, $str );
    fclose( $fp );
  }
 $dokument=file_get_contents( 'wms/admin/views/view' . $idview . '.php' );
 $contentdecoded=replace_between($contentdecoded, '[PHP]', '[/PHP]', $dokument  );
}

echo $contentdecoded;
?>