Call back youth around one (4)
I believe the answer is:
dial
'call' is the definition.
(both can mean to telephone)
'back youth around one' is the wordplay.
'back' says the letters should be written in reverse.
'youth' becomes 'lad' (lad means a young man).
'around' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'lad' placed around 'i' is 'laid'.
'laid' back-to-front is 'DIAL'.
(Other definitions for dial that I've seen before include "feature of old phone?" , "Laid up like clock-face" , "Meter face" , "Watch face" , "Ring the clock-face" .)