am not able to send data to phpmyadmin database
You never will be able to. phpmyadmin is a php script for administering MySQL databases, NOT a database.
Serial.print("GET http://localhost/data2_write.php?RFID_TAG_No=42:30:EB:10&SITE_NAME=BLOCK B\\r\\n");
A GET request does NOT contain a protocol, so the http:// bit is wrong. It does NOT contain a server name, and even if it did, the server name is NOT localhost.