Bob has you, ultimately, in his head (6)
I believe the answer is:
bounce
'bob' is the definition.
(thesaurus)
'you ultimately in his head' is the wordplay.
I cannot really see how this works, but
'you' could be 'u' (commonly used in online communication) and 'u' is found within the answer.
'head' could be 'bonce' (informal term for a person's head) and 'bonce' is present in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'has' acts as a link.
Can you help me to learn more?
(Other definitions for bounce that I've seen before include "Showing self-confidence" , "Exuberance; rebound" , "What a cheque may do if there are insufficient funds" , "Rebound; self-confidence" , "Spring back; resilience" .)