Everyday's a school day!
I just thought they linked via RPM.
Is the phase an additional call/option, or is it working in the background so to speak?
Speed and phase sync are usually two seperate M codes. I guess phase sync takes another 0.2 seconds or so, so if you were really chasing cycle time and didn't need it...
FWIW, the synchronisation doesn't work properly on my Doosan either, although it has no significant problems with acceleration*. On mine, when both spindles are sync'd and clamped onto the workpiece the sub is in constant overload and you have to perform the cutoff quickly or it will alarm out.
We have 2 lathes with fanuc controls (1 is a Puma 3100) and both will start cutting before the spindle has ramped to the correct speed. have always assumed its a fanuc issue.
I have two 16" chuck Victor slant beds, and they have g or m code called "Spindle speed arrival check" or something like that. The purpose of which is just to wait until the spindle as at the correct speed. I have very rarely needed to use it, but it exists for that purpose. I guess the keep relay that Paul mentioned does something similar under the hood.