When I first started working at a job, I used to work as an IT administrator. At one point, I even installed cat-5 cable through an entire 5000 sq. feet office building. That was a lot of fun as I had to access the office ceiling for a whole day.
Anyways, a Cat-5 ethernet cable is nothing more than “enhanced” phone cables. The phones usually use Cat-3 cables, which are slightly thinner wires and is more prone to electromagnetic interference.