See my earlier reply above for how to change the default primary line for the phone port to be the line port. You will need to use Expert mode on the Obitalk portal. Similar to the screenshot I have attached. You will have two tick boxes at the right hand end of the line. You need both to be unticked before you can change the setting.
If GV is configured on SP1, then the **1 prefix will probably already send outgoing calls to GV. If you really want to use **8 instead that is possible but needs more configuration changes.