Follow these guidelines to fix your access to the List Stacking dialer:
Go to your ‘Profile’ in the top right corner, and select ‘Manage Users.’ The list of users will appear.
Find your name and click the ‘Pencil’ icon. The edit window will open.
Click the ‘List Stacking Dialer.’
Enable the toggle on Dialer Access to grant access.
Click ‘Save Module Permissions.’