Ask your HR department for these accommodations. Tell them this is an Americans with Disability Act request for reasonable accommodations. Use these terms specifically and in writing. Something like,

"I suffered a concussion on (state date) that has been medically documented. I am now suffering from Post Concussion Syndrome. This leaves me very susceptible to excessive audio and visual stimuli. I have severely reduced ability to multi-task. Any attempt to multi-task created an undo burden that can cause me to crash and lose focus. It also has reduced my ability to maintain pace and persistence to some of the tasks asked of me. As a result, I need the following reasonable accommodations according to the Americans with Disabilities Act. I need more frequent breaks from certain tasks (list these tasks). I also need a way to work without frequent interruptions that cause me to loose focus requiring me to find a way to regain focus. "

You know the specifics.

The phone ringing may be able to be moderated.

Spending a day doing data entry sounds extreme. You need to ask for this to be broken up into manageable portions.

You qualify for protection under the ADA because your PCS has caused a limit to qualifying major life functions.

Hopefully, your HR department can come to your aid. Your ADA condition protects your job from retribution from asking for reasonable accommodations.

Remember to make these requests in writing or email and print and keep copies of the back and forth. Do not respond verbally. Keep this issue in writing. You might even say that you have read that this issue should be resolved in writing.

My best to you.