I’m not really sure how this happens. You are talking about the built in phone and contacts app right? If that is the case I would see if they are hiding somewhere on the phone. These are built in apps and to my knowledge, the only possible way you could get rid of the apps is to root the phone. Not really sure why you would get rid of those apps in the first place. If you can, I would back up any critical data then factory reset the phone. Make sure it is not linked to a Google account before you reset the phone or at the very least, make sure you know the Google account credentials as you will likely need these to do a full factory reset.