He phones the visitor (6)
I believe the answer is:
caller
'the visitor' is the definition.
(caller is a kind of visitor)
'he phones' is the wordplay.
I cannot quite understand how this works, but
'he' could be 'cal' and 'cal' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for caller that I've seen before include "One visits" , "Visitor" , "Someone phoning" , "Person on the line" , "One paying a brief visit" .)