Hardsynced squarewave and anti aliasing technics

Hi there,
May ask to you how to archive an hardsynced sware wave and the best practice to antialiasing,

I need to reset share wave phase at the beginning of the sound, or when a signal cross the 0,

Square wave classes that i know are only with initial phase variable.

Someone who want to share an oscillator good for?

Thanks a lot!

Gian