In music the term phrasing refers to the way notes are articulated and assembled into groups. A phrase is a group of notes that expresses a musical thought or idea. If a solo is likened to a paragraph of writing, a phrase would be one sentence of that paragraph.
Phrasing encompasses many factors that affect the way notes are delivered, including speeding up and slowing down, playing notes loudly or softly, accenting certain notes, the attack of each note, and more.
Another aspect of phrasing is where you choose to begin and end your phrases. If you phrase on the bar, you would begin your phrase on beat 1 of a measure and end it close to beat 4 of a measure. Or you could phrase across the bar, which means your phrase would begin somewhere in the middle of a measure and end either in the middle or at the end of a measure.
When you play a solo you're putting together phrases, or musical ideas, that begin somewhere, progress in some direction, and wrap up at the end with a sense of conclusion.