Contacts problems

There is no easy way to do it properly, and you need to be methodical. You will need to select the contacts you wish to keep and delete the others.

You could do it one of two ways - go through your list deleting those you don't want, or as you go down the list select those you want and preserve a copy in a folder on your Mac before deleting the entirety of your Contacts and importing back those you have selected to save.

What I would do, and assuming that your Mac and iPhone are using iCloud to sync, is to go through your entire list using your Mac, dragging to a folder on your desktop those you wish to keep (this creates a copy) . When you are satisfied that you have completed this delete the entire collection: Command and A to select all then right click and delete. I find the advantage in this is you have actively selected what you want to keep, rather than kept them by default in the process of rejecting those you don't want.

Then with a blank canvas import back to Contacts those you previously selected to keep. Just drag and drop all of them as a batch into the part of Contacts where your alphabetical list used to be.

But before you do anything export an archive of your contacts: Menu bar > File > Export > Contacts Archive and do a Time Machine backup.