A “remove all” button for employee contacts, or maybe the option to not receive text messages from employees that are assigned to an HR manager, or an expiry on messages that deletes them automatically after a certain period of time. At the point where you have 500+ employees they can send dozens of messages a day about their problems, which is what HR is for.
My game got to the point where I had so many contacts built up the bizphone would take several minutes to load (and crash the game on occasion) when clicking different options or managing employees. After spending a very long time clearing my contacts the issue was fixed.