contactsmojave
So with Mojave, Apple removed particularly LinkedIn and Facebook internet accounts and as a result my macOs contacts app now have LinkedIn group with hundreds of my LinkedIn contacts which I do not want to have in contacts app and I can't delete it.
Any way to remove LinkedIn group? (as well as Facebook group)
Currently the only way to do this is by synching your contacts via iTunes. It's not possible via iCloud. I also want this feature. Please leave Apple feedback.
I'm not sure if this will solve the problem exactly as you specified, but you can hide those 4000 contacts of customers on your iPhone with the steps below.
If your entire email's contacts are synced with your iPhone, you can choose to display only actual contacts and hide those email contacts with the Groups button in the Contacts.app in iPhone
For instance, this is a sample screen that could show when you touch Groups
Also, if you go to your Mail settings on your iPhone (Settings => Mail, Contacts, Calendars) and your Mail account, you can choose to remove your email contacts from your iPhone contacts by turning Contacts off in the picture below.
Best Answer
For account groups, you need to remove or disable in the preferences. In the "Contacts" app, go to the menu bar, "Contacts" then "Accounts..." those accounts should be listed. If so, you can remove or turn them off (uncheck the "Enable this account" box) there.