@jaseg The uC controls a DAC which sets the OCXO's tune pin voltage. There is definitely a delay (1s) between updates, but I think the problem is that I do the +/-1 every time the phase difference is +/-. So, if it takes 5 iterations for the phase diff to change signs, I'll end up with +5/-5 depending on the direction. Which is generally too much.
Today I intend to implement a PID controller...or something approximating one. Even just a P-controller would be a step up.