Well it depends. Are you putting them in as Phone messages and tasks? Or Memos. 

If Phone messages, you can always go to the individual matter, tasks, change assignee to that staff, and then look through completed and possibly filter by category as well. 

If Memos, What I would do is use the search term phone call and look on through based on that search term, especially if you are using the same sort of title and naming strucuture.