I’ve heard this a few times and it always feels dramatic in the moment. Short answer: no, phones being fully off is not a standard requirement for IFR or autoland. Modern aircraft are certified to handle passengers having phones in airplane mode, even during Cat II/III approaches in low visibility.
What probably happened is either airline policy being enforced extra strictly, or the crew being overly cautious during a very low RVR landing. Some crews still default to “everything off” when conditions are stressful, even if it’s not technically necessary. It’s more about reducing any possible distraction or unknown variable than a real avionics risk.
So yeah, understandable given the fog, but not an actual special IFR rule.
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