Quote from Option Trader:
I didn't know this. If so, that certainly does make it difficult to buy at the bid. However, for single leg orders, it certainly seems to me that they are able to achieve both simultaneously, i.e. to send to the exchange & they monitor other exchanges.
A good suggestion would be to have a public "spread book" available to all IB customers. Assuming that the customer wants his order to be shown, IB could display all of their spreads in real time to their customers (Think or Swim does this).
The CBOE now publishes their spread book (all spread orders working on the CBOE) only during market hours:
http://www.cboe.com/cob/cob.aspx
However, since IB is working most of the spreads upstairs in the black box, only IB customers will see it. It would thus make sense for IB to work spread orders on an exchange (i.e., the ISE or CBOE) so more people will be able to see these spreads and possibly trade against the spread order.
Therefore, it makes the most sense for option spreads to be sent to either the ISE or CBOE if it cannot be executed. Once the option order can be executed, SMART would cancel the order from the ISE or CBOE and then electronically leg the spread to get the execution (i.e., but 1 option on the PHLX, sell 1 option on the ISE).