If I bought an iPhone from someone who is now deceased how can I unlock the phone

If it has an activation lock, you can’t use the phone. If this person was a relative, you can try this: How to request access to a deceased family member’s Apple account – Apple Support (UK)

Angwill75 wrote:

I bought this iPhone from someone who is now deceased how can I unlock the phone

You probably can’t unlock the device. Without the Apple ID and password of the deceased owner you are out of luck. Sorry