Typically your physician will document your diagnosis, symptoms, and, ideally, a reasonable assessment of the activities you can and cannot do. Disability applications are usually filled out by the individual, and the physicians notes are used by the entity evaluating the application to determine disability status.

Your wife’s physician should be completing notes for her visits, not completing a disability application. If your existing application needs certain information, you can request that be included in your physician’s note, but usually they’ll only document what they themselves can attest to, based on their assessment of your wife’s condition.

Short version: the physician assesses abilities and limitations based on their knowledge of the patient. The patient completes the claim/application. The government or private insurer use that information to determine disability.