Can the landline phone be used in production halls for emergencies?

If you need a landline phone then it may be feasible - just think about how best to control it and minimise risk, e.g. corded rather than cordless, metal rather than plastic where possible, on your brittle materials register and sanitation schedules etc as appropriate.

as long as the foreign matter control and risk of allergen and micro cross-contamination are controlled properly, I don't see why not. I had a similar landline device in a high risk room in the past and we secured the device in a lockable SS box. This device was also in the pre-op checks for hygiene and foreign matter.