OK .. if it's an estate then the little aerial is used for both radio and phone ..
Haynes ... 12.19 section 21
Aerial - Saloon models
1 The aerial is integral with the rear heated
screen element.
Aerial - Estate models
2 It is recommended that the removal of the
aerial is carried by a Vauxhall dealer as the
operation involves the partial removal of the
load compartment headlining.
Aerial amplifier - Saloon models
Removal
3 Remove the rear seat cushions and back
rests as described in Chapter 11.
4 Where applicable unbolt and remove the
centre three point seat belt with reference to
Chapter 11.
5 Remove the rear headrests, then depress
the locking tabs and remove the headrest
guide sleeves from the seat frame.
6 Undo the securing screws and remove the
centre arm rest.
7 Carefully prise out the press stud fasteners
and remove the parcel shelf trim panel from
the vehicle.
8 Unscrew the coaxial cable connectors from
the side of the amplifier unit, the unplug the
power supply wiring connector from the front
of the unit.
9 Slacken and withdraw the securing screws
and remove the amplifier unit from the parcel
shelf.
Refitting
10 Refitting is a reversal of removal.
Aerial amplifier - Estate models
Removal
11 Open the tailgate, then work around the
periphery of the tailgate trim panel and
unscrew each of the securing screws. Lift the
panel away from the tailgate.
12 Unscrew the coaxial cable connectors
from the side of the amplifier unit, the unplug
the power supply wiring connector from the
front of the unit.
13 Slacken and withdraw the securing
screws and remove the amplifier unit from the
tailgate.
Refitting
14 Refitting is a reversal of removal.
HTH