I don't think anyone has a definite answer. In my experience if a device gives me a migraine in 15 to 30 minutes there is no way to use it for long periods. I once tried using a gaming PC that gave me migraine problems two days in a row during covid lockdown and I was with migraine for 2 weeks and couldn't use any device anymore.Is there not a risk of negative effect build-up? Examples:- I could use an iPhone 13 for nearly a week before my eye muscles strained so much that I had headaches. The iPhone 16 Pro Max was symptom-free for 2 days and nights until the third day when my eyes felt punched and I had a skull-splitting migraine! If your eyes and brain start to hurt, it"s your body telling you to stop.
I can't help but feel that screen protectors are just snake oil.......
The company notebook was causing me headaches after a couple of hours but I noticed that with a 30/60 minute break the headache would go away. So I insisted and managed to adapt and now I can work 8 hours with a slight headache after several hours but that goes away with breaks.
Back to the topic, we are talking about phones so if using it 30/40 minutes in a row doesn't cause problems, I would keep the phone and try to reduce the hours of use.