The "No Ghost" strategy for the Cerberus boss involves a specific sequence of actions to bypass its Ghost Phase.
During the fight, Cerberus activates a mechanism that spawns three Summoned Souls, which I refer to as the Ghost Phase. This phase is both resource-consuming and challenging to survive. As far as we know Ghost Phase is triggered by a mix of Cerberus' health and player aggression.
To effectively "dodge" the ghost phase, the following steps should be followed:
Note: It's important to note that after the 56-second timer has elapsed, it's most efficient to switch to the highest Damage Per Second (DPS) gear at your disposal. We guess that another internal timer of around 56 seconds initiates, and if Cerberus isn't defeated during this time, a new Ghost Phase will commence. This is why it's recommended to use Guthans for initial phase down to around 400hp, then switch to the highest DPS and specs once the timer has ran out.
Note: One crucial point is that if you strike Cerberus too soon (with a remaining second on the timer), you risk triggering an immediate Ghost Phase. It's vital to wait for the bell sound before attacking.
Checkout Fall_n explaining the method in this YouTube video, if you need more information - https://www.youtube.com/watch?v=G-ZBNA6XSxE&t=93s