I think if your Job Description changes and you have to manage more individuals the complexity of your job also increases. You should indeed get some sort of in

I think if your Job Description changes and you have to manage more individuals the complexity of your job also increases. You should indeed get some sort of increase in $$$ or promotion, ideally both. You may have to work a few months in your new role before your boss will consider a pay increase. While you wait, collect the facts and figures that show how your new role benefits the company. Decide the maximum and minimum you'll accept, then ask for a meeting.