Think of the way you talk - you form ideas into sentences, and at the end of each sentence, you pause. B.B. King plays guitar the same way. Listen to this mp3 clip of B.B. King's guitar solo on "Paying the Cost to be the Boss", paying attention to King's phrasing. Notice that King plays an idea, and pauses before continuing with another idea. Musicians who play wind instruments (trumpets, saxophones, etc.) are forced to play this way, as they have to stop and breathe. Guitarists don't have the same limitation, and often end up playing notes endlessly. The use of more "horn-like" phrasing, however, can be very effective - the pauses between riffs allow the listener to digest what they've just heard.
You may find that initially trying to incorporate phrasing into your solos is a difficult concept to master. Using the blues scale, practice playing a "riff" of five or six notes, pausing for a few seconds, then continuing with a new series of notes. Concentrate on making each short riff sound complete - try not to let the series of notes sound unresolved. This may be overwhelming at first, but as you continue to practice, your phrasing will grow stronger and stronger. Listen back to the mp3 clip above, and try to emulate B.B. King's approach.
