Phosphoric acid won't harm glass.
Both ceramic wall tiles and toilet bowls are "glazed". My understanding
is that they're fired once to set the clay, and then painted with a
glazing paint and fired again so that paint melts and forms a glass
surface on the hard clay. So, there's a thin film of glass on the
surface of both ceramic wall tiles and a toilet bowl. Phosphoric acid
doesn't harm that glass, so I don't see why it would do any harm to your
glass shower doors or glass shower surround.
Some shower door frames are made of aluminum. If yours are aluminum,
I'd test the phosphoric acid on it in an inconspicuous spot first.
(Oven cleaner (aka: sodium hydroxide or NaOH or "lye") will dissolve