He goes half a mile in a taxi (5)

'he' is the definition.

'half a mile in a taxi' is the wordplay.
'half a' suggests halving the letters.
'in' indicates putting letters inside.
'a taxi' becomes 'cab' ('cab' can be a synonym of 'taxi').
'mile' with half the letters taken is 'le'.
'le' going within 'cab' is 'CALEB'.

'goes' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.

Can you help me to learn more?