“Order by” result of “group by” count?

The easiest way to do this is to just add an order clause to the original query. If you give the count method a specific field, it will generate an output column with the name count_{column}, which can be used in the sql generated by adding an order call:

Message.where('message_type = ?','incoming')
       .group('sender_number')
       .order('count_id asc').count('id')