As you know, with mobile devices you may have multiple dialer applications installed, the default one coming with the device but some third party apps can also be a dialer (like for example truecaller).
Well, you can now configure your application protection policy to handle which dialer app will be used when a phone number is detected.
To manage the dialer app to use, create or edit your application proxy policy by connecting to your Endpoint Configuration Manager portal (https://endpoint.microsoft.com/) and access the AppsApp protection policies blade
Then create or edit an existing policy for either iOS or Android
Then the dialer application management option is available during Step 3 – Data Protection
You need to set the Send org data to other app to a managed application (not the default option set to All apps), then you will be able to define the dialer application to use when a phone number is detected