This splitter is intended for telephony, not for Internet (LAN). All ports are wired in parallel. This does NOT work for Internet! It may work randomly, depending on the connected devices and cable lengths. Passive (without power supply) splitters for Internet/LAN do not exist or cannot exist at all. If you want to "distribute" the Internet, you need a hub (obsolete) or a switch.

Take a switch as already written in another answer. These don't cost much more than a splitter and you have many more advantages than disadvantages as with such splitters.

Or do you really want to plug and unplug devices all the time? Are you sure you never, ever want to use two devices at the same time? So buy a switch, that's it.