How to restrict visibility of companies?

It's possible to differentiate access to CRM companies. Let's say that Sale Manager should see only his/her companies and not others.

There are steps to make such settings.

In CRM Administration, tab Companies create a new company attribute with JIRA user (or JIRA Group) type, for example an attribute "Sales Manager". See more: Set up Companies Directory
Restrict CRM permissions depending on that attribute. See there: Setting up Access to Objects
Open a Company card and set the attribute "Sales Manager" with needed JIRA user/users (group/groups).