Dipthong  
"oi"

 Phonics 84A

oi

sounds
like oil

boil

Bracket the (oi).  It sounds like "oy".

1.  br(oi)l

2.  join

3.  coin

4.  coil

5.  foil

6.  soil

7. uncoil

8.  airfoil

9.  topsoil