A distinctive or clever way of wording something, basically your personal little linguistic flourish. A good turn of phrase makes a plain sentence stick in people’s heads, whether it’s poetic, savage, or just dead accurate. It’s not full-on slang, more a poshish way to big up someone’s wording. Shakespeare had a few alright ones, to be fair.
"Our manager tried to call the pay freeze a team-building pause. Mate, that’s a turn of phrase worthy of a dodgy politician and a Tesco meal deal"