How can I add "Reward if found. Call..." to my lock screen in iOS12?

Thanks for your help. This is what I did: After checking the reviews for the apps, i decided to make my own lock screen from a photo. I took a photo of an abstract painting and went into Photos. Edited using the marker and text. You can drag the text box around and select the size and font that you put in it. I then saved the finished picture to an album called Wallpaper because you can't see which picture has text in the thumbnails. Also, your picture will be enlarged when the lock screen is formed so you can't make the text too large or too near the bottom of the image or it will be cut off when you form the lock screen.

Thanks for pointing out how the phone number can be used against me. I wouldn't have thought of that, but I am offering a reward for the return of the phone and would expect to meet with someone and give them cash at a Starbucks...