Okay, here is some insight from a guy who is nearly deaf. And, I don't use a phone anymore but did . . .
Telephone numbers have no context. They are essentially random numbers.
If someone says, "One, two, three, %*)^, #%&^." You can probably ascertain that it is, "One, two, three, four, five." Understanding, or a good guess, doesn't require the precise hearing of the words after "One, two, three." Telephone numbers are NOT like this.
I could fake hearing for years and years. We all do it, subconsciously. If we hear, "Good morning, %*)^ #%&^ *%^%, today?" We respond, "Fine, thanks! How are you?"
A few years ago, it became just too much "#%&^" and with a rising inflection at the end of the sentence. It could be "Good morning, how are you, today?" Or, "What the hell are you doing here?" Could be anything. I don't remember when understanding telephone numbers went out the window. Earlier century . . .