It’s harder to hear tone of voice over the telephone. Phone lines convey what the phone company thinks is the minimum information needed to understand speech. It doesn’t convey music well, apparently. It’s not very good for people speaking a language they’re not very fluent in. I have trouble recognizing whose voice it is or even sometimes whether it’s a man or a woman; this can be embarassing. It’s not lying to say “I can’t hear tone of voice very well over this phone connection.”
That makes a lot of sense.