Hey Abgp,
Thanks for using Apple Support Communities! I understand after saving some Contacts on your iPhone, they eventually disappear. I definitely understand needing to get to the bottom of this and ensure that all your Contacts are saving as expected. I am happy to work toward a resolution with you.
To start, let's check Settings > [Your Name] > iCloud to see if Contacts is enabled there. If so, let's also check Settings > Contacts and make sure you have iCloud as the Default Account selected there.
Let's also follow the steps in the link below to refresh your Contacts and see if you're able to view your missing Contacts: Get help using iCloud Contacts, Calendars, or Reminders
Thanks again, and have a great day!