One of the Chappell brothers at church with workers for plainsongs (9,6)
I believe the answer is:
gregorian chants
'plainsongs' is the definition.
('Gregorian chant' can be a synonym of 'plainsong')
'one of the chappell brothers at church with workers' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
'of' could be 'o' and 'o' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'church' could be 'ch' (common abbreviation) and 'ch' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?