The official mobile apps have special tools for disabling contact sync and deleting imported contacts. It can be useful if you imported a bulk of contacts by mistake.
When you use these commands, all the imported contacts will be deleted and re-synced based on the current phonebook of the device.
Go to Settings > Privacy and Security > Data Settings.
Go to Settings > Privacy and Security > Contacts.
Sync Contacts – general contact sync.
Delete Synced Contacts – this action will remove your imported contacts. If Sync Contacts is enabled, the current phonebook will be exported.