Much like the trophy for getting a Fluxation 10 times on Command Spritnite, you will follow the same process for this. The only difference is you need to equip a talisman with 'Support Bonus' as one of the attributes. Without that, the Fluxation only occurs to command spritnites.
A Fluxation has a chance of occurring when you use Momentum with a tech or combo attack (to use momentum, the circle to the right of the player name needs to have a white dot above it, you can then press
just as the move starts to add Momentum). There doesn't seem to be any information on when this can occur. It just seems random. So keep using Command Spritnites with your Momentum and the trophy will come at some stage.
One tip is to equip as many Support spritnites on each active character and a talisman on each that has support bonus. You obviously need at least 1 Command spritnite so you can do momentum attacks.
I suspect you either won't get them when used on a weaker enemies, or significantly less chance, as I went for this after I had already got above level 50 with each character. I went through the whole of the Lost Lands and only got 1 fluxation. It finally came when I was going through some of the final side quests on an enemy that took multiple tech attacks to finish off. There is a person at the location described in the following trophy guide that offers to increase all enemies to your level. This may help if you are struggling: