Which is an activity in the 'Problem control' phase of problem management?

Problem Control. Problem control activities include problem analysis and documenting workarounds and known errors.

Just like incidents, problems will be prioritized based on the risk they pose in terms of probability and impact to services. Focus should be given to problems that have highest risk to services and service management.

https://www.bmc.com/blogs/itil-problem-management/#:~:text=2.,probability%20and%20impact%20to%20services .