Final answer:
The call placed by another physician is most likely to require the physician's immediate attention.
Step-by-step explanation:
The incoming telephone call that is most likely to require the physician's immediate attention is Call placed by another physician.
When a physician calls, it usually indicates an urgent matter that requires immediate attention from the physician receiving the call. It could be a request for a consult or advice on a critical patient.
On the other hand, calls from equipment salespeople, patients requesting prescription refills or scheduling appointments, and patients requesting laboratory test results can typically wait and be addressed during regular office hours.