He doesn't have any scheduled absences. Based on Instagram posts he seems to have been out for the last few performances but I don't believe it was planned.
phantom1978 said: "Thanks for all the replies. Wish they would post them like they do with the Christine alternates."
They don't post his schedule because, aside from illness or vacation, he is scheduled to appear in all performances. Unlike Christine, there is no alternate for the role of the Phantom.
==> this board is a nest of vipers <==
"Michael Riedel...The Perez Hilton of the New York Theatre scene" - Craig Hepworth, What's On Stage