Screentime on child’s phone but not laptop

Hello - my son has a phone and laptop both set up with his Apple ID. We have been using screentime through familysharing to limit phone use which works well. Is there a way to designate screentime limits for just his phone? At the moment it also limits his Apple laptop and I don’t see way to differentiate by devices. In screentime it shows up as just his iPhone. Would rather he not change laptop to separate Apple ID. He’s happy to change any settings on laptop. If I can’t separate, will need to stop using screentime as will interfere with schoolwork. Thank you!