confirming approach phase is not irreversible.
The CONFIRM prompt is there because it is very likely to push the LSK where the ACTIVATE appraoch phase is when passing from one performance page to another. Should this occur, all you have to do is not confirm and problem solved. But if you do press the LSK because you really want to activate the phase, then why on earth should you think it twice??
The FMGS, in NAV mode and speed managed , will activate the phase automatically, without even asking!
Even if you activate it inadvertently, it is no big deal. It is not like switching off an IDG. fly selected until you can go head down and recover the phase you want.
Oh, But in this thread we have drifted sooo much...