The idea of the phonic coils was to not use a sync pulse, but apply the whole video signal to a set of coils that acted on a toothed wheel attached to the motor shaft. As long as there was sufficient low frequency video contrast, this would hold the motor at the right speed - but the phase could vary.
Regarding sets with manual speed controls (and no synchronization means), they were found to be too difficult to adjust, such that the picture would only be in sync for a few seconds at a time. Modern experiments confirm this.
Check out the Narrow Band TV Association:
http://www.nbtv.org/
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here's a picture of a Baird replica with phonic wheel
http://www.earlytelevision.org/baird_kit_copy.html