This is the thing Phalanx being a complex electromechanical piece of kit has more bits to go wrong. Yes the Humble Oerlikon or Bofors has a simpler system but they have manual controls that can work (in the older models) without power and have a crew on them to sort out any stoppages. The principle of KISS should be applied to the last layer of the airdefence bubble. Yes have the missiles and phalanx but a few more crew served manual weapons have their place.
Can the Naval Minigun mount elevate enough to provide AAAD? and maybe a few .5's on ships would be useful additional airdefence.