Dallas rallied from a 17-point, third-quarter deficit and was up 86-80 with 5 minutes to play. But the Mavericks went four minutes without scoring while the Suns climbed back into the lead.
Eric Bledsoe had 20 points, nine assists and six rebounds for the Suns. Morris added 19 points and 13 rebounds.
Chandler Parsons scored 19 points and Amare Stoudemire 16 for Dallas, which has lost all three games against Phoenix this season. Monta Ellis was 4 for 22 from the field, including six straight misses down the stretch.
The Suns were coming off a 117-102 victory at Houston on Saturday night.