I see in the documentation that Outbound Routes have a priority:
Outbound routes have a priority. If a dialed number matches the pattern in two outbound routes, the route with the lower priority rating will be used to place the call. The priority is determined when you define an outbound route: The Route Position list in the Route Settings section determines the sequence in which outbound routes are tested, until a match is found.
However, I cannot find this “Route Position” setting anywhere on the outbound routes settings page?