If the link to click the Company field/column is not available in the activity list, this means the custom role has no permissions to "Company".
1. Log in to NetSuite using Administrator role.
2. Navigate to Setup > Users/Roles > Manage Roles.
3. Edit the custom role.
4. Go to Permissions tab > Lists subtab
5. Add "Companies" and set the level to "View" (or Full)
5. Click Save.