A person who plays the triangle is often referred to as a "triangle player." In orchestral settings, they may also be called a percussionist, as the triangle is a percussion instrument. While there's no specific term exclusive to triangle players, they are typically part of the broader category of musicians who specialize in percussion instruments.
scalene triangle
An equilateral triangle
equallateral triangle equallateral triangle
a scalene triangle
equilateral triangle
Taytum Pow
There is no particular phase to describe it as per my knowledge. It's usually known as Triangle Player. e.g.: John Deacon of the rock group Queen assumed the role of a triangle player during the band's live performances.
A "harmonicanist" is what a person who plays the harmonica is called.
A person who plays Scrabble is called a Scrabbler. (unofficially)
A drummer or percussionist plays the drums.
accordionist
harpist
a baritonist
guitarist
A saxophonist.
Guitarist
a cymbalist