How do I retrieve my deleted contacts
How do I retrieve my deleted contacts from my phone
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It all depends on where those missing contacts were stored.
If no account was used with Contacts app, then they would have been stored locally, on the device. In that case, restore your iPhone from a backup you made prior to the incident.
If you do use iCloud to sync your contacts, here is document with instructions how to recover accidentally deleted contacts; If you accidentally deleted your calendars, bookmarks, or contacts from iCloud:
https://support.apple.com/en-us/HT205018
If you used other account than iCloud to sync your contacts, contact with whomever supports your account for help with instructions how to get back data you are missing.