Head of Logistics phoned up boss (5)
I believe the answer is:
gnarl
'boss' is the definition.
(thesaurus)
'head of logistics phoned up' is the wordplay.
'head of' suggests taking the first letters.
'phoned' becomes 'rang' ('ring' can be a synonym of 'phone').
'up' says the letters should be written in reverse (in down clue: letters go upwards).
The initial letter of 'logistics' is 'l'.
'l'+'rang'='lrang'
'lrang' written backwards gives 'GNARL'.
(Other definitions for gnarl that I've seen before include "Lump, growl" , "Rough lump (on a tree)" , "Tree-swelling" , "Lump or knot in a tree" , "lump of wood" .)