Goq, you were right, but you were also wrong. Sometimes being right doesn’t MAKE you right. IMO, you kind of made a mountain out of a molehill, and I happen to agree that “yes” is not a proper phone response(though it works for when an aveil answers the phone or it is Tisha B’av).
The person you spoke to, no doubt rightly thought you to be a little uptight, and it was probably a little inappropriate to be giving mussar to someone about something rather subjective after all, and even more so that you were at work. Supposing this person took great offense and spoke to your boss about it (or are you the boss?) It really was a very small issue to make such a big deal. I do understand how you feelm, though, but I would have handled it differently. I have learned in life to pick and choose my battles.