Correct usage of "to coin a phrase"

To coin a phrase did originally mean to invent a new phrase, but its use now is almost always ironic.

It often seems to be an author's way of excusing him/herself for using a cliche.

I'm sure the reporter knew perfectly well the implications of using to coin a phrase, and it wasn't an "ironic" usage in the sense that people say this when trotting out a cliche. It's a tichy (tongue-in-cheek) example of typical British understatement.

Barry Kilby (manager of Burnley Football Club) has said more than once that he wouldn't bet the ranch on the outcome of an upcoming game. The reporter is slightly niggled by this, since the standard (particularly in the UK) expression is bet the farm. She's even more niggled because we don't even have "ranches" in the UK - but we do have a preponderance of foreign (including American) managers of our football clubs.

Personally I think the reporter is taking two or three good-natured pops at what she sees as legitimate targets, while showing her own skill at writing by doing this in so few words.

Edit: Having not actually followed OP's link to the newspaper report itself until now, I've just somewhat sheepishly changed the gender of my pronoun references to reporter Suzanne Geldard.

The OED confirms the current meaning, but with no suggestion that it once meant anything else:

an expression commonly used ironically to introduce a cliché or a banal sentiment.

The earliest supporting citation is dated 1940. The entry for ‘coinage’, however, includes its figurative use to mean

The (deliberate) formation of a new word, etc.

As other respondents have said, it's nearly always used jokingly to pretend that the speaker has invented the phrase. However, I've never seen this usage - where the speaker gives credit to someone else (in this case Kilby) but also claims that she's coined the phrase. Seems a bit strange.