Slur:
A slur is a curved line connecting two or more notes on the same staff, indicating that they should be played smoothly and connected, without any separation between them. It creates a legato effect, where the notes blend together seamlessly. Slurs are often used to group notes that form a melodic phrase or to connect notes within a phrase.
Phrase:
A phrase in music refers to a group of notes that form a musical idea or unit. It is similar to a sentence in speech, with a beginning, middle, and end. Phrases are often defined by musical elements such as melody, rhythm, harmony, and dynamics. They can vary in length and complexity and can be characterized by their melodic contour, rhythmic patterns, and phrasing gestures.
While slurs are used to indicate how notes should be played within a phrase, phrases themselves are larger musical units that encompass several notes, including slurs and other articulation markings. In essence, slurs contribute to the phrasing of the music by connecting notes within a phrase, while phrases are the larger units of musical expression that give shape and meaning to a piece of music.