Sphere holds a key to allow access again (7)
I believe the answer is:
readmit
'allow access again' is the definition.
I can't tell whether this definition defines the answer.
'sphere holds a key' is the wordplay.
'sphere' becomes 'remit' (both can mean someone's area of work or activity).
'holds' means one lot of letters goes inside another.
'key' becomes 'd' (musical key).
'a'+'d'='ad'
'remit' enclosing 'ad' is 'READMIT'.
'to' is the link.
Can you help me to learn more?
(Other definitions for readmit that I've seen before include "Again accept" , "Let in a second time" , "Welcome back" , "Take in again" , "Let back in" .)