"portrait sketch" is correct and usable in written English.
You can use it when you are referring to an artistic representation of a person's face, usually made with pencil, charcoal, or paint. For example, "The artist spent hours perfecting her portrait sketch of the woman."
Sir Frederic William Burton (1816-1900), Portrait sketch of George Eliot, 1865.
The artist friend who announced casually that if you'll come down to his studio some time next week, he'd like to try a portrait sketch of you.
George Washington visited there in 1779 and sat for three-quarters of an hour for the portrait sketch from which this engraving is derived.
He made a lackluster sales pitch to a passing group of tourists using one of the few English phrases he knows — "Portrait sketch?" — but the visitors kept moving.
Here, the figures are subordinated to the style with which they are depicted, and the examples include a lively William Merritt Chase portrait sketch and a vibrant lithograph by Rufino Tamayo.
With that canvas as its centerpiece, the display includes landscapes of Peconic and elsewhere, a charming portrait sketch of Wiles by his son and an interesting selection of documentary material.
The portrait sketches were expanded because of their great popularity.
To have one's portrait sketched takes twenty minutes and costs twenty dollars.
He later developed an enthusiasm for an American singer, Cher.Mr Farmelo's sympathetic portrait sketches Dirac's unhappy family background.
I think Rathburn is – on balance – an anti-Scientology hero, but we deserve the more ambiguous, troubling portrait sketched here.
At the time, he was an aspiring history painter who made his living with small portrait sketches of fellow expatriates and wealthy tourists.
