Susannah's partner on the phone with father in Caribbean island (8)
I believe the answer is:
trinidad
'caribbean island' is the definition.
(I've seen this before)
'susannah's partner on the phone with father' is the wordplay.
I cannot quite understand how this works, but
'partner' could be 'n' and 'n' is located in the answer.
'father' could be 'dad' (dad is a kind of father) and 'dad' is present in the answer.
This explanation may well be incorrect...
'in' acts as a link.
(Other definitions for trinidad that I've seen before include "West Indies island" , "Island linked to Tobago" , "Port of Spain island" , "English-speaking island off Venezuela" , "W. I. island" .)