ศาลาชุมนุม

As a Brit, I always see 'ph' pronounced as 'f' - physics, physical, etc, although I know the etymology shows those two words originate from Greek.

You say, "The rule rule of the RTGS system is that a written Thai term is spelt as it is pronounced"
So for example, where does the "H" come from in พัทยา or ภูเก็ต - Phatthaya, Phuket?
I must be missing something obvious here.