One of the possible causes of extreme slowness and application crashes on a phone is low or insufficient storage space. This can affect the performance and functionality of the phone, as well as prevent new applications from being installed or updated. The technician should check the storage space on the phone and see if there is enough free space available for the diagnostic application and other operations. The technician should also advise the customer to delete or move any unnecessary or unused files, apps, or data from the phone to free up some space. Reference: https://partners.comptia.org/docs/default-source/resources/a-core-1-content-guide (page 10)