The Phantom title card says "While you are docked, the Ghost can perform primary weapon attacks from its special firing arc and, at the end of the Combat phase, it may perform an additional attack with an equipped (turret). If it performs this attack, it cannot attack again this round."

Whose turret? One equipped on the Ghost, or one equipped on the Phantom?

It's the Ghost that can attack with an equipped turret weapon.

Yes, you can put a turret on the Phantom too, but it won't be able to fire that turret until after it deploys from the Ghost (at which point the Ghost loses its special rules from having a docked Phantom).