You need to filter aliasing before it occurs in the signal, because you
can't filter the aliased frequencies out of an already aliased signal. Put
your phasor in an up-sampled poly~, followed by a lowpass/brickwall filter.
There are different filters you could use like butterworth or FIR. I'm not
sure what's best.
If you just want anti-aliased oscilators use saw~/tri~/rect~
I have made a butterworth low-pass filter, tl.butterlp~. Butterworth
filters have a flat frequency response in the passband. I also have a
more expensive filter CPU-wise: tl.crossover4~. That is a fourth order