As a young phone guy I was taught about "Tip and Ring", the two connectors on the 1/4" mono phone plug.
Back then there were PBX trunks that were "ground start" where you'd need to apply a ground momentarily to the "ring" side of the line in order to "start" the dial tone.
So, polarity was critical throughout the connection all the way from the Central office to your premises.
40 years gone by I've seen/installed mechanical, electronic, digital, and now VOIP cloud systems. Few industries have seen such massive transformation. Now it's all about LAN, POE, Broadband, Servers, and SIP endpoints and softphones, none of which existed when I started.