If it's only 20 employees and want something quick and easy, I'd just do a Contact or Custom List. Since you only want to show 3 fields (which could actually be rolled into 2), I would lean more towards the custom list with a renamed Title field as your Phone field and then a Person or Group field for both Name and Presence. Set the column order in your view to show the new Person or Group column first, and then the phone number column.
This won't be synced to your AD in any way, so it will need to be maintained, but you will be able to have this set up and running in SharePoint Foundation in less than 5 minutes.