Gave my old iPhone 7 to my dad last year. How do I remove it from my list of devices now without deleting his data?

Last fall I gave my dad my old iPhone 7 & set up an Apple ID for him. Consumer Cellular walked us through transferring the SIM card from his Tracfone to the iPhone to keep his contacts' phone numbers. That all went well. Recently he received a notification on the iPhone 7 for a security update and was prompted to enter his Apple ID, but his password wouldn't work. Now I realize that his phone still appears in my list of devices.

When I click that phone in my list of devices, I see the option, "Remove from Account." I'm concerned that if I remove it from my list of devices, then the data he's accumulated by using the phone over the past 6 months will be deleted. We live in different states so can't troubleshoot this problem together in the same room. Could you please tell me how I can remove the iPhone 7 from my list of devices and associate that phone with his Apple ID without deleting his photos, texts, and emails from the phone? Thank you for your help!