Confused teen should phone if coming in (8)
I believe the answer is:
entering
'coming in' is the definition.
('enter' can be a synonym of 'come in')
'confused teen should phone' is the wordplay.
I cannot really understand how this works, but
an anagram of 'teen' is 'ente' which is within the answer.
'phone' could be 'ring' (to ring on the phone) and 'ring' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'if' acts as a link.
Can you help me to learn more?
(Other definitions for entering that I've seen before include "Starting" , "Going inside" , "Going/coming in" , "Coming in" .)