iPhone activity showing up on another phone

Figure out who owns the Apple ID being used.

On the other phone, do this: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch

Then, have the person who will be using it, set it up with their ID. They can create one during the setup process if they don't already have one.

nabeel115 wrote:

thanks! But how do I stop sharing?

Stop using the same Apple ID on both phones. Sign out on one and create another Apple ID if needed.

https://support.apple.com/en-ca/HT204316

Stop sharing an Apple ID.

Family Sharing does not share this content. Same Apple ID is the only explanation.