Can you use a phone cable as a Ethernet cable?

Maybe, depending on what you mean by "phone cable." Those intended for home use probably won't work (the connectors aren't really even compatible), but those meant for 8-pin office phones might work.

If you're not sure the cables are compatible, it's probably not a good idea to try it; you could potentially damage your hardware.

No ethernet cable are not phone cable and only look the same. The ethernet plugs are larger