I think you will run out of power before you run out of room.
I have one as well, I know the mountain lite came with a 1.25" lug 136" track and my Venture had the same, it was great.
I think you could easily go 1.75" as there were stock sleds with that tunnel with that track. but they also had heat exchangers so maybe the Phazer has even more room.
The stock I believe is a 9 tooth driver, the 136"x1.25" sleds have a 7 tooth driver which will give you some more low end to turn a bigger lug.
Good luck! lets see some pics of that unit! there's some of mine in a thread lower in this section. I have had mine since I was 12 lol