That's not how contacts are set up. You can have two contacts "Joe Smith" and "Sam Jones" and enter "Johnson Trucking" as the company under each contact. The people app doesn't support multiple names. You'll need to come up with a workaround using existing fields, but the phone will only display certain fields on the caller ID.
You could make the 'name' the company name, and then have the two employees listed in another field like 'title' or 'notes'. If they have different phone numbers you could also list each phone number under the company, and then give the phone numbers a custom name (instead of home or mobile) and enter the two employee's names. You can do the same with email addresses for each.
ie...
Name: Johnson Trucking
phone:
800-555-1212 : Joe Smith
800-555-1213 : Sam Jones
email:
jsmith@jtrucking.com : Joe Smith
sjones@jtrucking.com : Sam Jones