What happen when your iPhone 6s Plus keeps freezing?

What happen when your iPhone 6s Plus keeps freezing?

You upgrade to an iPhone 7.

Replaced it with an iPhone 8.

I would first reboot it a few times. If that doesn't work, I would then backup everything important and then perform a factory reset, installing the latest version of iOS. If that still continues, then it might be a hardware problem, which is difficult to diagnose/fix without the appropriate knowledge and equipment. In that case, I would just get rid of it and buy a newer phone.