Stock jetting is 143.8. With a totally stock Phazer, you should be able to run 140's no problem. 135's would work, but I would be very careful on colder days. Phazers are VERY sensitive to outside air temps. When running lean on cold days, vary throttle position often, never running steady-state in any one throttle position for long. You run it steady-state in a lean spot in the carburation, and you will squeak a piston for sure. Unfortunately, Phazer carbs are not very tunable, other than pilot jet and main jet. This leads to uneven air/fuel mixture throughout the throttle/rpm range.
Built a LOT of the little hair-dryers back in the day. Still have a soft-spot for them!