Singly in order (3,2,3)
I believe the answer is:
one by one
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">singly in order</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for one by one that I've seen before include "How queue's served" , "Individually placed order" , "Singly in order" , "Queen's autobiography?" , "separately" .)