So phone line when it’s 2 pair UTP is also known as Cat3 and you actually brought up something else interesting, the connector also doesn’t determine what the cable is doing either, you can use an RJ45 connector with cat3 cable and the right pins populated to pass Ethernet (up to 1000FX if I remember right) just as you can use 2 pair of a cat5 cable to replace cat3 cable in a pinch.

Back to switches though, a L3 switch is called that (or called a multi-layer switch) because it’s performing functions at multiple layers, I’m just trying to make the distinction that a switch and functions involved in switching does not operate at nor use any parts of the L3 protocol stack as switches do not view network traffic in packets but instead operate using and physical addresses and frames. The same physical device may do both but its import to understand that the device is using different components and logic to perform both functions (for example, a switch forwards frames based on the MAC/CAM table), the reason this is important is that it helps understand how things like VLANs work. Also, while I would agree that in the consumer space a router is 99% for a WAN connection that is definitely not true for routers (or even routing) as a whole, there are way more reasons to use a router between two private networks than just between a private network and the internet (which is what I assume you mean by WAN but that is also not always true).