Encourage possibly to deal with a back number (4,2)
I believe the answer is:
lead on
'encourage' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Perhaps you can see a link between them that I can't see?
'possibly to deal with a back number' is the wordplay.
'possibly' indicates an anagram.
'with' means one lot of letters go next to another.
'a back number' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'deal' is an anagram of 'lead'.
'lead'+'on'='LEAD ON'
Can you help me to learn more?
(Other definitions for lead on that I've seen before include "Entice" , "Deceive in fun" , "Show the way inside" , "Take for a ride" , "to come first" .)