CiviMobile App error when editing phone
Mine is still in testing, but yes, also seeing API errors on mobile app start. CiviCRM 5.14.1, Drupal 7.67.
There has been a new 3.1.1 release of CiviMobileAPI since your post you may want to try? I'm still seeing an error on app start with it.

Not sure about your CiviMobile, the app on play is com.agiliway.civimobile? Otherwise I don't think this: https://civicrm.org/extensions/civimobile/version-20 is required, or at least, it's an old dev and not related to the current API?