actually, I often practise this way - but starting from the end! ...
.....if you practiced each bar of a piece separately, one at a time, until it was perfect, and then when you had done this for every bar and mashed it all together, would it be more effective than practicing in a phrase?
According to Chuan C. Chang, https://members.aol.com/chang8828/contents.htm"Start learning the piece by practicing the most difficult sections first. The reason is obvious; it will take the longest time to learn these, so they should be given the most practice time. If you practice the difficult sections last and then try to perform the piece, you will find that the difficult part is the weakest and it will always give you trouble. Since the ending of most pieces is generally the most exciting, interesting, and difficult, you will probably learn most pieces starting from the end. For compositions with several movements, you will most frequently start with the end of the final movement."//Depp