How do I wipe and recycle old iPhones without affecting original owners' iCloud data?

Without the Passcode or users Account credentials, you won't be able to wipe the phones at all. If you could, no it would not remove what someone stores in iCloud. Since you won't actually be able to wipe the phone without the credentials required to get in the phones to even do so, you can safely recycle them at your closest Apple Store and you won't need to be concerned about the data on the phones anyway.

daneilleL wrote:

The phones where the data was deleted aren’t connected to cellular networks or wifi. The iOS system is too old to connect to my home wifi and there are no sims in them. I just wanted to get that stuff off the physical phone before I destroyed them. Otherwise I would have just reformatted them using the reset option.

Resetting the phones according to proper procedure would have disconnected them from iCloud early on in the process, so that erasure of local data on the phone did not affect synchronized copies of the data.

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Disconnecting the phones properly from iCloud synchronization before doing local deletions would also have spared the owners' iCloud data.

But you had to go in and do the one thing that guarantees that if any of the phones were doing synchronization with iCloud, they are now waiting to synchronize deletes with iCloud.

See what you need to do to wipe an iPhone in this link --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

I think you'll see you need more than just the Passcode.

“ I have deleted photos, contacts, text and voice mail messages from the phones”

That was exactly the WRONG thing to do. If that phone ever connects to the internet his data will be deleted from iCloud. Put a hammer through it to be safe.

daneilleL wrote:

I have deleted photos, contacts, text and voice mail messages from the phones, is this enough?

I hope you didn't do that on a phone still synchronized to iCloud. When you delete photos on a phone that is connected to iCloud Photos, it doesn't just delete them from that phone. It deletes from iCloud and from any other devices synchronized through iCloud.

daneilleL wrote:

I’m actually unsure why there is any data on those phones given they aren’t connected to wifi or a network.

Because iPhones store a lot of data locally – whether or not that data is also synchronized through the network.

It sounds like you've never heard of the concept of using a phone to play music or view photos in places where cellular data is switched off or unavailable, and Wi-Fi Internet service is also unavailable.

As Lobsterghost said, there was no need. With a passcode on, the data was safe without any intervention.

Now you deliberately deleted it, the danger is it might connect to a Wi-Fi one day. Destroy it now, and tell your friend never to trust anyone with their Apple ID password no matter how much they trust you.