For Phantom, I highly recommend that you go with orchestra center, somewhere between rows BB and K. As might be expected, most of this section is designated as "Premium Seating", so these seats can be pricey. The mezzanine overhang starts around row J, so if you go much further back than that you will miss half of the chandelier ascent/descent and all of the Phantom's appearances on the catwalk above the proscenium.
I've never had a good experience from the front or rear mezzanine at this theatre. It's a relatively large house and the upstairs seats feel very removed to me, as if I'm watching the show from outside, through a window. By contrast, the front orchestra feels incredibly immersive, as if you are part of the action rather than simply a spectator. If you cannot get seats in the center of a row and must choose to be more on the house left or house right, I recommend house left, if only for the blocking during "Stranger Than You Dreamt It".
==> this board is a nest of vipers <==
"Michael Riedel...The Perez Hilton of the New York Theatre scene"
- Craig Hepworth, What's On Stage