Would Somerville have used Force Z differently?

Would it have been different if Somerville, rather than Phillips, had commanded Force Z?

Probably: his caution and regional experience suggest he might have based the force back at Ceylon and used it more defensively.

The Indian Ocean looked less dangerous before Force Z was destroyed, so an earlier appointment there might have appeared comparatively quiet. Somerville already knew the region and understood prewar thinking about air power, battleships, and deterrence in the Far East. His caution makes Ceylon a plausible preferred base rather than an exposed commitment close to Malaya. The conclusion remains counterfactual, but it ties a different basing choice to Somerville's documented experience and command temperament rather than assuming the ships alone would change events.