The 27-year-old is entering the final season of a four-year, $50-million contract originally signed with the Miami Heat during the 2016 offseason.
Phoenix acquired Johnson in a midseason deal with Miami. He averaged 11.1 points, 4.2 assists, and four rebounds across 13 contests for the Suns.
After starting 12 games at the point for Phoenix, Johnson could receive some competition from first-round pick Ty Jerome.
The Suns tied for the second-worst record in the Association last year at 19-63.