Good afternoon Butchcessna,
It sounds like you might have iCloud Contacts enabled on your iPhone X, but not your iPad.
If that is the case, make sure you back up your iPad now so that you have a copy of all of your contacts.
Back up iPad
If you have a Mac, it would be a good idea to have a second back up your iPhone and your iPad on your computer as well.
How to back up your iPhone, iPad, and iPod touch with your Mac
Can you think of any activity you may have been doing when the number of contacts changed? What made you open the Contacts app to notice this was happening?
How much storage space do you have on your iPhone and in iCloud?
What's the difference between device storage and iCloud storage?
Let us know the answers to these questions and any other information you can provide about your issue, and we'll do our best to help.
Take care.