Clob Handle In Custom Type In PHP

I created a custom type what it has a clob member variable:

CREATE TYPE custom_type AS OBJECT(
c_type INTEGER,
c_number NUMBER(38, 8),
c_varchar2 VARCHAR2(4000 CHAR),
c_clob CLOB,
[code]........

The inserting and updating works with constructor: ... custom_type (to_clob('foo')) . But if the data is longest than 4000 characters then the PHP isn't access to it.

So:
The normal case:
$sql = ("INSERT INTO table ( clob_field ) VALUES ( EMPTY_CLOB() ) RETURNING clob_field INTO :clob");
$stid = oci_parse($conn, $sql);
$clobdescr = oci_new_descriptor($conn, OCI_DTYPE_LOB);
oci_bind_by_name($stid, ':clob', $clobdescr, -1, OCI_B_CLOB);
oci_execute($stid);
$clobdescr->save('more than 4000 chars');
...

This case:
I tried:
$sql = ("INSERT INTO table ( ctype ) VALUES ( custom_type(EMPTY_CLOB()) ) RETURNING ctype.c_clob INTO :clob");
$stid = oci_parse($conn, $sql);
$clobdescr = oci_new_descriptor($conn, OCI_DTYPE_LOB);
oci_bind_by_name($stid, ':clob', $clobdescr, -1, OCI_B_CLOB);
oci_execute($stid);
$clobdescr->save('more than 4000 chars');

ORA says: "ORA-00904: CTYPE.C_CLOB: invalid identifier";

How to?Or how to access with any solution?