You can apply a constant force downward. Technically force=mass*acceleration so the gravity force for a specific object would be that. But the physics units are flawed in the behavior so a constant like 50 would work.
Alternatively you could set the y velocity to self.physics.velocityY+500*dt which would just apply an acceleration directly
Thanks for the response. I tried that and it works, but the problem with it is that the gravity 'speed' never increases, so it feels pretty floaty.
I tried doing that but also multiplying/adding a variable that increases over time to it to make the gravity speed increase the longer you fall, but none of my solutions have really gotten the desired affect. Any ideas?