no worries.
The managed speed is taken from the FMGS phase
Takeoff phase has V2
Climb phase has climb speed.
Cruise phase has cruise speed (well, ok its mach, not speed)
Descent phase has descent speed
Approach phase uses O/S/F speeds
There are 2 ways to get into approach phase.
1) go to PERF page on mcdu, press "activate approach phase" then "confirm".
2) fly over a little "D" in a circle which appears on nav track, in nav mode, which from memory is 15nm from touchdown (Could well be wrong)... then it automatically activates approach phase.