Sangoma Talk app - how do I view a contact groups from two PBX deployments?

Hi,
I know what I want to do but don’t know how to get there.
First some background.
I have two PBX deployments (PBX-1 and PBX-2) In each deployment I have done the following.
PBX - Contact Manager.
I created an internal group named ‘Phonebook’.
PBX - User Manager - Contact Manager tab
For each user I wanted to be seen…
Show In Contact Manager Groups: ‘Phonebook’
Viewable Contact Manager Groups: ‘Phonebook’
Favorite Contact List: Inherit

I have Sangoma Talk app installed on an iPhone which is registered with PBX-1. In the Talk app, when I click the Contact button, I am shown the list of users from the
PBX-1 ‘Phonebook’ group. This is good.

Now in the Talk app, I also want to see the list of users from the PBX-2 ‘Phonebook’ group.

How do I setup PBX-1, PBX-2 and the Talk app to show the list of users from both PBX-1 and PBX-2?

Thank you,