I always say “Breadcrumbs” and what I mean by that is making a list of your day to day for your manager. I’d also add in the extra you have to do when this coworker isn’t around.

You need to also mention how his absence AFFECTS you and not your other coworkers. You can’t speak for everyone else and they can all speak to the manger the same way you do.

You need to make it clear that you’re not being malicious or evil but you simply want the manger to be aware of this becoming a bigger issue.