Constantly duplicating contacts

Contacts should be in one, and only one, email account, for example iCloud.com, Outlook.com or Gmail

They do not need copying or manual syncing from Mac to iphone or vice versa. They are in one place up in the cloud and your Mac and your iphone just mirror them.

You say you merged them which suggests multiple sources and I think that is your problem.

In Settings, Contacts, Accounts ensure only one account has Contacts turned on

On the MAc in System preferences, Internet Accounts also check only one account has Contacts turned on

Then you have the task of removing duplicates and you will have to look further for tools or methods to do that, but at least the duplication should stop now.

Read the whole post.

as I said earlier what you SHOULD have is:

In phone Settings, Contacts, Accounts ensure only icloud account has Contacts turned on

On the Mac in System preferences, Internet Accounts also check only icloud account has Contacts turned on

Obviously the Mac and the phone must be on the same iCloud (apple ID) account

But you don’t currently have that so

ANYTHING COULD HAPPEN

The likelihood is you will have 38000 contacts everywhere so decide if that is what you want.

To prevent that you have a massive job of thinning out icloud.com and I don’t know a way to do that easily . There may be an app available to help

If you have the big number on the mac there is an app AB Export that can export them as CSV file from the Mac’s Contacts app.

Backup everything first.

Good luck, you will need it