Call chap up on phone, in the end (4)
I believe the answer is:
name
'call' is the definition.
(as in calling or naming someone something)
'chap up on phone in the end' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'on' says to put letters next to each other.
'in the end' says to take the final letters.
The last letter of 'phone' is 'e'.
'man' written backwards gives 'nam'.
'nam'+'e'='NAME'
(Other definitions for name that I've seen before include "Handle" , "By which one is known" , "Identification" , "celebrity" , "Monicker" .)