The Broomfield side had clawed their way back into the match before conceding 26 points in the final quarter.
Cumnock had high hopes of winning which would have seen them leapfrog their hosts in the table but the loss now makes their survival chances in the league harder.
Phoenix enjoyed a strong wind at their back in the first half and used it to good effect to keep the game in the Cumnock half. Scrum-half Jayson McMillan made a break from the base of a scrum but his pass back inside was spilled and the chance was lost.
Phoenix served notice of their intentions, mixing their play up by bringing their powerful forwards into play before moving it wide where they had some dangerous runners. However, it was weak tackling from Cumnock that allowed Phoenix to score their first try as the defenders fell away, giving the home team a clear run to the line.
Cumnock nearly fired straight back with stuart hunter and Alan Smith combining in the centre to release Martin Thomson who drew the last man and passed to Gregor McMillan. The pass dropped just short and the winger knocked on with the line at his mercy, allowing Phoenix to clear.
They were made to pay moments later after some more powerful drives from the Phoenix forwards opened up space out wide for their winger to run through for a score, leaving Cumnock twelve points behind at half time.
Cumnock knew they had to make up for their slow first half and powerful running by Graham Montgomery and Jamie Thomson made ground for the team. However, it was Phoenix who drew first blood with their outside-centre producing a classy bit of skill with a delicate chip over the top of the defence after picking the ball of his shoe laces. The ball bounced kindly for him as he crossed the line for his side's third try.
The signs of recovery were still there for Cumnock and they responded with a try of their own though David Kerr. The Cumnock captain broke the defence off a shortened line-out and had enough pace to outstrip the covering defence to touch down.
This seemed to spur Cumnock on and they were rapidly back on the attack with stuart hunter again well to the fore and Jamie Hodge making several strong carries. A loose clearing kick from Phoenix was gathered by mark linden who powered forward before slipping a nice pass to Jamie Thomson. The quick ball was spun wide and slick hands by front rows Graham Montgomery and paul miller released Gregor McMillan who beat his man on the outside to score. stuart hunter was on target with the kick, bringing Cumnock back to within five points of the Glasgow club.
They set about closing this gap further and worked their way back to within five metres of the line after a driving maul from a line-out. They won a penalty after Phoenix halted the drive illegally but then saw the penalty reversed after a Cumnock player spoke out of turn to the referee.
Phoenix saw this as their cue to regain the initiative with some fast flowing counter attacking rugby. Cumnock's discipline went out the window as they gave away penalty after penalty and Phoenix took full advantage, running in four rapid tries as Cumnock saw two men sent to the sidelines for ill discipline.
Cumnock's late collapse when it looked like they might have fought their way back into the game was typical of a lot of their season and they are now left with four remaining league games to ensure their survival. Currently they are sitting eighth and they face a crucial tie away to ninth placed Clydesdale next weekend.