Phrasing is a difficult habit for beginners to deal with. Nevertheless, some students which are already studying “performance level” have difficulties to manage a phrase. Don’t think that the habit of phrasing will come naturally and easily by playing and practicing piano for years. When I was watching competitions in school music festival, I could always observe that students have no idea of what is a phrase (and of course, they did not receive any prizes). In fact. teachers have the responsibility to teach students to make good use of combination of arms, wrists and fingertips.
1) You can develop your habit by very short slurred groupings and practice “Down-Rotate-Float” movement. The following is one of the examples of short phrasing exercise.
2) Listen carefully to the tones that you are producing. Do notes link to each other tightly with similar tone quality using one wrist movement? Or you are applying accents / up-down motions from time to time?
3) Singing is probably one of the most useful methods. Try to sing along with your piano playing so that you can notice any differences in between.
4) Listen to pieces played by strings. You can search it in Youtube and I show the following video to my students very frequently. Many of them understand what is a phrase and legato playing immediately after watching it.
Here is the recommended video, “Vocalise” Op.34 No.14 by Sergei Rachmaninoff (1873-1943).