A quick reminder from the RSI website (https://robertsspaceindustries.com/about-the-game) describing what different hardpoints on your ship are capable of doing.
Hardpoints
Every ship has hardpoints on which a variety of different weapons can be mounted. Each hardpoint has a classification. A lower classification can always be mounted on a higher classification hardpoint, but not the other way around.
CLASS 1
Fixed Gun. This is your standard forward facing laser, neutron cannon, particle gun, etc.
CLASS 2
Articulated Gun. Think the guns in Freelancer or the smart weapons found in later Wing Commanders. Class 2 hardpoints are rarer and more expensive, but they allow guns to rotate on an arc rather than fire point blank.
CLASS 3
Pylon. This is where you mount missiles, ECM units, radar pods, drop tanks, additional ammunition, special scanners, etc.
CLASS 4
Turret. Uses the same fixed guns as class 1, but mounted in a separate area of the ship which may be crewed by another person. Turret slots can also mount pylon-type weapons (i.e. a tractor beam or a chaff dispenser.)
Class 5
Manned point defense turrets, generally mounted on larger ships and capital ships.
Class 6
Heavy manned capital ship turrets â€" used for ship-to-ship combat.
Class 7
Spinal mount lasers â€" heavy hitters that are effective against medium and large ships.
Class 8
Capital ship cannons â€" extended range heavy weapons used for capital ship battles in space
FYI. Class 9 slots are automated point defence turrets. They have been so far anyway.
What's confusing about those Class 9's is that as per the other Class numbering format, the larger the number, the more massive the hardpoint/attachment they house.
So how does the number 9 fit into the whole Hardpoint Class numbering scheme. Generally point defense systems are multiple small lasers, compared to the Phoenix with a single one.
Perhaps it's just meant to be a catchall. It'll likely change later as they add new things.
It's designed to target small fighters and missiles so I guess it could just refer to the automated nature of it.
Weak but it might be true.