Phase train AND accessory transformers?

No, Since these are two seperate circuits phasing does not matter in this application.

Since the output phase is not significant, where you plug them in is also not significant.

I recommend that you phase the accessory transformer, also. I believe that some accessories such as the horse and cattle corals get their common from the outer rails

Denny.

The time that phasing comes into play is if the command AND hot are somehow tied together.  Just having the commons out of phase won't be an issue.

I am of the opinion that all transformers should be phased, since on a layout unexpected "things do happen." Phasing is such a simple task that there is no need to try to avoid it, and you gain flexibility for the future.

From a shock hazard standpoint, phasing the transformers is better.  If there is any connection of the commons, out-of-phase transformers will have a voltage equal to the sum of the individual voltages across the hot-to-hot leads.  If you should accidentally touch an accessory feed and a track feed at the same time, the 36 volts or so may be enough to cause a hazardous shock, especially if your body moisture is high on a warm high-humidity day.

Yes, it's just "good practice" to phase all transformers on a layout.

And boy at my age , do I need flexibility!

I don't disagree with phasing all the transformers, but in this specific case, the fact that they might not be won't cause any issues.  However, the shock potential is there at 36-40 VAC, so that's a factor.