It’s not the “English R” but kind of the Spanish or Italian one.

More specifically: it's similar to the R in Spanish "pero" and Italian "correre", a tap; unlike the RR in Spanish "perro" and Italian "correre". In English typically when you hear the trill it's for /r/, among Scottish speakers.

I didn’t read the context so this might be old news, but you can even read it as nothing since all the letters can be silent (as much as they can be fish)

G as "gnaw", H as "hour", O as "rough", T as "listen", I as "business". Done, ghoti = Ø.