This method of phasing under blocks makes several things extremely inconvenient or impossible. For example, entering phantom mode on a one-block-deep bridge is needlessly dangerous; you can't charge Rogue sneak attacks while hiding as a phantom; you can't enable vampire invisibility without falling through blocks; et cetera. Changing this keybind would be hugely beneficial.

Try shifting and jumping

I know what your saying you try to do the classic bridge and you fall through it, while it is true most bridging is done in the Nether and End some overworld bridging with the sun out can be a problem for a Phantom. Now you could wait till night but that's not fixing the problem that's just avoiding it. As such I agree about this Enhancement and I think the best approach is to utilize the secondary power key as seen in Extra Origins for example as the Descent button.

I recommend this since none of the base set use the secondary power key, it would be a very easy thing to implement, and it would mean that addons will not require binding a key to the secondary power out of the box. Knocking out 2 problems at the same time, and putting more emphasis on the secondary power keys use in the base set.