How to create this sort of board in Phaser 3?
The question is, to do what with this board?
I mean you could just use this image and put it as a sprite into the game. Done, board in the game.
Not much interaction possible, but it would be there.
If you want to be able to recolor each triangle of the board, I would create one triangle sprite and then 8 of them in a line, rotating them as needed to form the board.
That way, every sprite can change and you can detect touches or clicks on the individual sprites.