Wallpaper disappeared

Hi Christine Altieri,

We appreciate you reaching out to us.

First, let’s check for a software update and make sure that you are running the latest version of iOS.

While it isn't inherently assured that an update will resolve the issue, updating to the latest software version for your device can help isolate potential software issues. 

Kindly secure a backup and update.

1. How to back up your iPhone, iPad, and iPod touch
2. Update your iPhone, iPad, or iPod touch

After the update, please add the wallpaper back.

1. Make sure that you previously set up Face ID on your iPhone. To change your wallpaper from the Lock Screen, Face ID must clearly see your eyes and the areas around them.
2. On the Lock Screen, touch and hold your Lock Screen to open your wallpaper gallery.
3. To select a wallpaper you already created, swipe left and right. To add a new wallpaper, tap the Add button .

You can use the article below as a reference.

Change the wallpaper on your iPhone - Apple Support

Take care!