Old woman stops to phone man in one's group (7)
I believe the answer is:
chagall
'man in one's group' is the definition.
The definition suggests a singular noun which matches the answer.
'old woman stops to phone' is the wordplay.
'old woman' becomes 'hag' (hag is a kind of old woman).
'stops' is an insertion indicator (stopping can mean blocking a gap).
'to phone' becomes 'call' (synonyms).
'hag' placed inside 'call' is 'CHAGALL'.
Can you help me to learn more?
(Other definitions for chagall that I've seen before include "Marc -, twentieth century Russian-born French artist" , "Marc --, Russian-French artist" , "He painted" , "Russian-born painter" , "Marc --, Russian artist" .)