The extra permissions are required by the Enpass for extra functionalities offered. No matters, even if we have to consume a minimalistic capability of permission set, you'll be prompted to grant permission for whole set. As you've asked, here are the details of the extra permissions required by the app at the time of installation.
Access to text messages - This permission is used to send an SMS directly from Details screen of Enpass item. Used by the fields of type Phone Number.
Browser - As you may know Enpass for Windows Phone has an inbuilt browser for the autofill functionality. So, in order to access the browser components, this capability is required.
Phone - To use the call/phone services of the device, this functionality is required. It is also used by the fields of type Phone Number from the Details screen.
Also there are two more capabilities which Enpass requires which are:
Network access - It is used when 'Backup and Restore over WiFi' service is used by Enpass. In this case, Enpass acts as local server and the data can be backup or restored by the Web Browser on the PC.
Removable Storage - As there is option for Backup and Restore from the Local Storage of the device, this permission helps Enpass to access the removable storage and store or access the Enpass data from there.
Hope this information is helpful to you. In case of further queries, please contact us again.