pg-affected-rows () only runs on the LAST SQL STATEMENT executed. If you compound several statements together then pg_affected_rows might not return what you expect.
For example:
<?php
$result = pg_query ('BEGIN; INSERT INTO foo (bar) VALUES (\'baz\'; COMMIT');
echo (pg_affected_rows ($result));
?>
will cause 0 to be printed, because the last statement executed by Postgres was COMMIT, which doesn't affect any rows.
I haven't tried this so am not certain it works, but you SHOULD be able to get the row counts you want if you split your queries up.
For example:
<?php
$result = pg_query ('BEGIN; INSERT INTO foo (bar) VALUES (\'baz\';');
echo (pg_affected_rows ($result));
pg_query ('COMMIT;');
?>
should allow you to get the number of rows affected by the previous query. I haven't tried this yet though, so don't count on it.