One who calls cheerfully for spirits; just the right amount (5,6)
I believe the answer is:
happy medium
'just the right amount' is the definition.
'one who calls cheerfully for spirits' is the wordplay.
I cannot really see how this works, but
'one' could be 'me' (a setter might use 'one' to humourously mean 'me') and 'me' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for happy medium that I've seen before include "avoidance of extremes" , "Sensible middle course" , "Sensible middle way" , "pleased spiritualist" , "satisfied spirited interpreter" .)