Option 1:
Dibden is some distance from Southampton centre, so I would suggest you catch a train. The central station is almost opposite the bus station. The nearest station to Dibden is Beaulieu (pronounced 'Bewlee') Road but not many trains run there. If you can't catch one to there, go to Ashurst or Brockenhurst instead.
Once there you will need to catch a taxi.
Option 2:
Find someone on the same phase 3 who would be willing to give you a ride!