In some sources the name of this site is written as ‘Dol-y-Gamfa’. Presumably this has been abbreviated to Dolgamfa over the years.
The name ‘Dol-y-Gamfa’ means something like ‘place of the crooked meadow’, and if you look at the plateau that the circle sits on, this is very appropriate. I’m pretty certain that the farmstead to the south of the circle shares the same name.