Me parece que tu problema es que no tenes bien configurado el tns_names.
te transcribo la descripción del error:
Cita:
Iniciado por Oracle SQL Codes ORA-12538 TNS:no such protocol adapter
Cause: The protocol adapter requested (by way of the (PROTOCOL=) keyword-value pair in a TNS address is unknown. If the supplied address is typographically correct then the protocol adapter is not installed.
Action: Install the protocol adapter or correct the typographical error, as appropriate. Note: if the supplied address was derived from resolving the service name resolution, check the address in the appropriate file (TNSNAMES.ORA, LISTENER.ORA, or TNSNET.ORA).
Seguro que podes conectarte via SQL*Plus desde el servidor donde corre tu php??
Hasta luego.
;)