Follow these simple steps and you’ll be set in minutes.
Open Settings > Tap Apps

Search for Phone

Go to Default calling app

Choose Mobile Office in the list of eligible Default Calling Apps > tap Mobile Office to select it. A check mark indicates it’s active.

Make a test call > Open Contacts, tap a contact with a phone number. Mobile Office should open and will go ahead a place the call. Confirm call connects and appears in Mobile Office Recents Page.
Mobile Office only launches when you tap a phone number from your Contacts. If you dial manually, use the iPhone Recents page (unless you've used Mobile Office to call before), or ask Siri to call someone, the call will go through your regular cellular line instead.