That leaves me with a strong impression you had a competent bunch of plumbers.

One reason to pass messages verbally along the chain is that way, everyone involved knows what's happening. Point-to-point with cellphones can leave folks in the middle not knowing what's going on, which is not ideal with high-pressure anything. It also ensures that you know where everybody is, and that the apprentice has not wandered off or [been] overcome by an errant and unexpected jet of water.