You can share Imported contacts with users by using Delegate Contacts option, but it will only allow to share upto 25 users.

  1. In the Admin console or from user, Select Contacts 
  2. Select More option, In drop down list select Import
  3. Upload .Csv file and Import
  4. Now select newly Imported contacts tab (appear under My Contacts tab at right side)
  5. Select all and click Group icon 

  6. Under this tab Select My Contacts and Apply

Now Follow steps for Delegating contacts

  1. Select More option 
  2. In drop down Select Manage delegation settings
  3. Enter Id's you want to share My contacts in Invite People tab
  4. Select Send 
  5. Now user can see shared contacts under Delegated contacts