How can I stop iPhones sharing images

WLM21

I have an old iPhone (maybe a 6 or 7) which I only use when out and about kayaking or paddleboarding. There's a PAYG SIM inside.
Now, I have received a hand-me-down iPhone 11 from my wife, which I have put in a cheap contract SIM. It has a good camera, so I tend to use that now to take images ... I note today though, that these images are being shared between the two phones. I don't need this, so how do I disable this function please?
many thanks for any advice

Getferret

Are both phones signed into the same Apple ID?

WLM21

Getferret said:

Are both phones signed into the same Apple ID?

Yes.
I am not really an Apple person, so asked my daughter (an Apple fan) to set everything up for me. I had read somewhere that you can only have one iphone on a single AppleID, but she said not ... so it was set up that way.

Should I maybe visit the Apple store, explain the situation and just set up a completely new ID

DullGreyGuy

Settings ->  AppleID (top option) -> iCloud -> Photos and you can then turn off the synching 

Getferret

If you want to prevent newly captured photos from being synced to all iOS devices using the same Apple ID account, go to Settings app, scroll down to Photos tap on it, and then turn the My Photo Stream feature off.

Getferret

Two devices can sign into the same Apple ID but one device cannot be signed in two Apple ID’s at the same time.

I suggest creating a new Apple ID for yourself.