Depending on your application syntax the socket can be found at like this (localhost can be replaced with 127.0.0.1 if needed):
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PHP applications that are aware of sockets are few, and most typically try to connect to a port. You will have to craft a way to define the one you want to use for your particular app. Some let you put it in a variable, some will just need you to add it after the hostname or ip (localhost:3309), some will just assume 3306 and just ignore anything else.