I've never ridden without a lockring but I have with a loose one. The cog slips, no matter how hard you crank it down. Then again, your mileage may vary depending on the quality of your cog, grease, hub threads and amount of torque you applied to the hub or to the bike when riding. At 48x16 with just resisting, the cog would slip after much tightening.

I've never tried it with my Phils so I can't say but I wouldn't run that risk anyway.