Assuming you're using postgresql:
$query0="insert into table1 values('abc',123)";
$query1="insert into table2 values ('xyz',789)";
$conn = pg_connect("connection params");
$res0 = pg_exec($conn,"begin");
$res1 = pg_exec($conn,$query0);
$res2 = pg_exec($conn,$query1);
$res3 = pg_exec($conn,"end");
should work.