Considering your components (the Phanteks Enthoo Pro M case and the Corsair H100i v2 Liquid CPU Cooler), you are only left with one vacant fan slot.
The Liquid CPU cooler already has 2x 120mm fans included. The case already has 2x 140mm fans pre-installed (1x in the front intake and 1x in the rear exhaust). You can mount the Liquid CPU cooler (with the 2x 120mm fans) either in the front of the case (as intakes) *or* at the top of the case (as exhausts), whichever you prefer.
Note that, typically, the radiator of a Liquid CPU cooler with its fans working as intake will significantly lower the temps of your CPU but tends to increase the general interior temperature inside your case for the other components. On the other hand, the radiator of a Liquid CPU cooler with its fans working as exhaust will significantly lower the general interior temps of all other components inside your case but tends to not maximize the cooling effect for the CPU.
If you do decide to mount the Liquid CPU cooler in the front, you would need to move the pre-installed 140mm fan to the top. You can still install an additional 140mm beside it on top, which will both work as exhaust fans.
If you decide to mount the Liquid CPU cooler at the top, you don't need to move the pre-installed 140mm fan on the front. You can still install an additional 140mm at the front, which will both work as intake fans.