I am unable to get email to connect to my IMap server using the iPhone 6+ with IOS 8.3.

The telco (Telstra Australia) loves telling me that they do not block ports.

Either the telco is blocking ports or the phone is blocking ports.

Can a hotspot connected computer route port 993 requests through the phone without blocking within the phone?

I have no trouble routing port 80, 443 requests through the phone as a modem, and also direct from Safari, however any other ports through Safari on the phone, or a hotspot connected computer fail to connect.

Is there a firewall on the iPhone that needs to be configured to allow additional ports through, and if so, how would it be configured.

If the phone is connected via wifi it has no issue connecting to any of the ports it needs to, it is only an issue when connecting over 3/4g networks.