Be sure to see @MultiTech 's video cited in @diogolupcosta 's reply. That clearly illustrates that you’re not connecting your app directly to your Contacts as a data source, but rather syncing information between your Contacts and a partial replication in an ad hoc data source.
You need a table in your app connected to a data source where you store the contact info you want to see in the app. To initially populate the table, you may need a one-time effort to either manually populate the data source or create an app action and associated script to do it all at once.
If there are changes to your contacts not made via the app, then your script needs a function to periodically update the data source directly. You can create a time-driven trigger to do that.