1. Configure SP1 with the 2nd Anveo number.
2. Then click the gearwheel icon at the right hand end of the SP1 line, immediately to the right of the trashcan. If you have two gearwheels on that line, not the one containing a red E. You will have a box with two lines near the top containing "Primary Line for Outgoing Calls" and "Incoming Calls Will Ring On". On each line click as required to have ticks for Phone 2. Click the Save button.
3. Repeat step 2 above but for SP2. Click as required to have ticks for Phone 1. Save.
4. After automatic reboot(s) your OBi should be configured as requested and the summary box should show that.
Obviously if you want to swap which phones use which numbers in and out, just tick the other boxes.