Here are the steps to troubleshoot when your phone’s wallpaper doesn’t change:

1. Check your Wallpaper settings
   
   1. Go to Settings > Wallpaper on your phone
   2. Make sure you are allowing your phone to access iCloud photos
2. Check your Storage Capacity
   
   1. Go to Settings > General > Storage & iCloud Usage > Manage Storage
   2. Make sure you have enough storage left
3. Restart your Phone
   
   1. Hold down the sleep/wake button and drag the slider to turn your phone off completely.
   2. Hold down the sleep/wake button again to turn the phone back on.