In alphabetical order in what way?
If you view contacts by display name, it automatically puts it in alphabetical order.
If you view by email address, it also automatically puts it in alphabetical order.
However, if you mean by cutom name, this cannot be done as plus uses the view by e-mail address, so contacts are in alphabetical order by email address.
This was also suggested here
Suggestion for Plus! - Custom contact names in alphabetical order...