On 2014-02-18, Judy Miller wrote:
It always seems I have the wrong diameter headphone jack when I need one.

Since adapters exist, why do they make headphone jacks different
diameters anyway?

Cell phones used to have 2.5 mm plugs, because cell phones used to be tiny.

Early AMPS (analog mobile phone service) cell phones in the 1980's were
essentially suitcases, and were called "car phones". By the early 1990's, cell
phones had shrunk to the point that they looked like household cordless phones.
A race was on for phones to be smaller and smaller. The smaller the phone the
more "status" it showed. Within about a decade, by the 2000's, phones became
ridiculously tiny. These tiny phones used 2.5 mm headphone jacks to save
space. Every cubic millimeter counts in a compact design.

The trend now is for phones to be larger, because they are now essentially
small tablet computers, and the screen size matters. Nobody wants to use
a 1.5 by 2 inch screen.

These modern smartphones tend to have the usual 3.5 mm (or 1/8") jacks that you
also see on computers.

I.e. long story short; your phone is probably outdated.