ldap_unbind kills the link descriptor.  So, if you want to rebind as another user, just bind again; don't unbind.  Otherwise, you'll have to open up a new connection.(PHP 4, PHP 5, PHP 7, PHP 8)
ldap_unbind — Desliga-se do diretório LDAP
| Versão | Descrição | 
|---|---|
| 8.1.0 | O parâmetro ldapagora espera uma instância de LDAP\Connection;
  anteriormente, um resourceldap linkválido era esperado. | 
ldap_unbind kills the link descriptor.  So, if you want to rebind as another user, just bind again; don't unbind.  Otherwise, you'll have to open up a new connection.