most any riser for the yamaha flat post steering stems and 7/8" will work.
heres some things to consider with the phazer:
cable length. how high can you go? you are limited as you wont find any cable extensions for your throttle or brake. plan accordingly.
wiring, speedo, and tach cables. probably enough slack in the speedo and tach, you may be splicing wires.
due to the design of the phazer, when you raise the bars, your also raising the pharing with the headlight. not a big deal here, but you increase the air flow to the rider. you may need to make something to block the increased air flow.
depending how much increase your looking for, the rox pivoting riser in about a 2" would be one i would consider. even thats iffy with your existing cables. some creative re-routing may make it happen.