Hello jonesie,
Welcome to Apple Support Communities!
We want to help resolve the issue with the password prompt asking for his password.
We’ll need to learn more about this to help isolate and resolve the issue.
Sometimes this happens when the iPhone is using the App Store with another Apple ID, or did so previously. Have you downloaded any apps or used the App Store using his Apple ID in the past? Do you see any other messages or errors that might indicate why it's asking for the password?
To check to see if this may be due to apps that were previously downloaded, on your iPhone go to the App Store > Tap Account on the top right. From there, if you scroll down do you see a list of apps that are waiting to be updated? If you tap update, are you prompted to enter the password for his Apple ID? If so, any apps listed there that prompt for his Apple ID would need to be deleted, then downloaded from the App Store using your Apple ID.
Before doing so, if you are concerned about any data loss, we'd recommend reaching out to the developer of the apps in question to inquire about data saving options: How to contact an app developer - Apple Support
If you restart your iPhone, does the issue remain after? To restart your iPhone, check out: Restart your iPhone - Apple Support
We hope this helps to further isolate and resolve what might be causing the password prompt.
Cheers!