Although you see arguments both ways, there is a minor concern about fire safety when placing a battery operated device exactly over a switch box unless it was designed for that purpose, which the Phillips was not.
Consequently most people do one of three things:
One) as you mentioned, simply mount the Hue dimmer switch on the wall near the original switch. A nice variation of this is to replace the existing single gang switch with the double gang plate and put the Hue dimmer switch on top of that. This is my own personal favorite. This picture is not my house, but it’s something I want to do some day:
Two) put a blanking plate over the original switch and then mount the dimmer switch on top of that, but then the original switch is no longer usable.
- put a wooden box over the top of the existing switch which can be lifted up if you need emergency access to it, and then put the new dimmer switch on top of that. Or use 3-D printing to print a plastic box of the right dimensions.
Any of these can work, it’s really just a matter of aesthetic preference.