After one of the asynchronous functions (pg_send_query(), pg_send_query_params()...) has been used, pg_transaction_status() will always report PGSQL_TRANSACTION_ACTIVE, no matter if a transaction was started or not.
Even after the first call (or all valid calls) to pg_get_result() the transaction status will stay PGSQL_TRANSACTION_ACTIVE, until either
- a synchronous function like pq_query() was used, or
- another call to pg_get_result() was made, which returns false.
Note: calling pg_free_result() does not change anything.

<?php
  $conn = pg_connect("dbname=publisher") or die("Could not connect");
  $status = pg_transaction_status($conn); // PGSQL_TRANSACTION_IDLE
  pg_send_query($conn, 'SELECT 1');
  $status = pg_transaction_status($conn); // PGSQL_TRANSACTION_ACTIVE
  $res = pg_get_result($conn);
  $status = pg_transaction_status($conn); // PGSQL_TRANSACTION_ACTIVE
  $res = pg_get_result($conn); // false
  $status = pg_transaction_status($conn); // PGSQL_TRANSACTION_IDLE
?>

This function is implemented in C, so there's no way to mimic it in SQL for older versions of PHP.  But you can mimic some of the functionality by using a wrapper which keeps track of when you begin and commit/rollback transactions.