Mk 15 Phalanx was designed so that it could be used as a stand-alone system. It can for example be bolted to the deck of any ship, even those that lack any kind of combat systems. Just plug it in and it is ready to go. So the applications include not just combat vessels but auxiliaries such as tankers, amphibious ships, transports and cargo vessels. There is no other equivelent gun system in the west. The American/Dutch/French Goalkeeper like Phalanx has its own onboard sensor package for autonomous operation but it requires deck penetration and thus can not be easily applied to ships that were not designed for it. Goalkeeper has a more powerful weapon with greater range and lethality and can track more targets than Phalanx though. The Chinese have a system, the Type 730 which is practically a carbon-copy of Goalkeeper.
The Italian Dardo and Swiss Seaguard not only require deck penetration for the weapon mounts but also depend heavily on the ships own combat command system for target data and fire control. The ships Target Indication Radar for example is the systems primary search element but it can also take data from the ships ESM system or an IRST while target tracking and fire control is by an off-mount electro-optical director. These systems are more massive than a stand-alone solution and naturally require much greater ship integration but have the advantage of much more powerful sensors locating higher up on the ship and the ability to handle many more targets at much greater ranges.
As an anti-missile system Phalanx was intended to be temporary - a sotp-gap solution until RAM was fielded, but RAM was more than a decade late so Phalanx became a fixture on many ship classes and for far longer than ever intended. In the 1980's the British Royal Navy conducted a study on the effectiveness of various anti-ship missile defenses and determined that against an Exocet-type target (relatively slow and unsophisticated) Phalanx would likely not achieve a kill until the target approached within 300 meters of the ship. For Goalkeeper the kill range was 800 meters. This is important because at ranges of less than 1 km even if the target is destroyed, fragments from it will still be travelling fast enough to pepper the ship (like a huge shotgun) and could potentially put the ship out of action like in the USS Worden incident off Vietnam. The RN stopped buying Phalanx and Goalkeeper after that. But to be fair, neither of these systems were intended to be a ships primary defense against missiles but rather its last-ditch defense, when everything else had failed.
Today Phalanx in the USN is no longer employed primarily to engage missile targets but is retained for use against small surface craft. To this end surviving installations are fitted with Infra-red camera's for identification and accurate tracking of small fast targets on the surface.