Final answer:
During the planning phase of an audit, obtaining an understanding of the client's risk assessment process is the most likely procedure to be performed. This is because it helps in identifying potential risks of material misstatement.
Step-by-step explanation:
The audit procedure most likely to be performed during the planning phase of an audit is obtaining an understanding of the client's risk assessment process. This step is crucial as it helps auditors to identify where there might be risks of material misstatement due to error or fraud. During planning, auditors typically do not test transactions or evaluate the reasonableness of accounting estimates, as those are often performed during the execution phase of the audit.