You can set below property to export user fields in CSV format :
# Input a list of user attributes that will be included when exporting users
# to a CSV file. You can include custom fields by adding the prefix
# "expando:" to the attribute name.
#
users.export.csv.fields=fullName,emailAddress,expando:phone
# Input a list of user attributes that will be included when exporting users
# to a CSV file. You can include custom fields by adding the prefix
# "expando:" to the attribute name.
#
users.export.csv.fields=fullName,emailAddress,expando:phone