I traditional high volume call centre with 100+ employees is different smaller centres. Assuming it's one of those:
Absence management, sickness lateness, return to work, conducting investigations and disciplinary hearings for absence.
Performance management, quality checks, call listening, coaching reviews, 121s, spot feedback, training new processes, team briefings.
Conduct issues, behaviour management, sorting out squabbles from the team WhatsApp group no one is supposed to have, canteen enemies, fights and affairs etc
Complaints, taking escalated calls and managing ongoing more complicated issues that front line advisors can't do. Approving credits and gestures of goodwill.
Productivity, explaining to your bosses why x minutes we're lost from your team's productivity yesterday and how you will improve. Stopping Steve from having a shit at work every day, after he's just got back from his lunch break and is signed back in on company time for instance.
Giving ideas to management for how to improve things for customers and staff.
It can be a thankless job. I've done it for 20 years and progressed to Head of Contact Centre roles. The money is pretty OK in the right places, but awful in others. I see Call Centre Manager roles advertised in NW for as low as £28 but would expect it to pay £40-50k for 100 people sized centre or a regulated environment like banking.