Greetings Looper543,
Welcome to the Apple Support Communities!
From your question, I understand that you accidentally deleted a playlist from your iPhone and after connecting that iPhone to your computer, it appears that that playlist is missing from iTunes as well. I also realize that you have tried to get the playlist back by using an .xml file, but it didn’t work.
One potential solution that may help you here would be to try and load a previous iTunes Libraries folder to recover that playlist. To complete this task, please follow the instructions located in the attached article below. Keep in mind, as explained in the article, that any changes you made to your library after the date of the iTunes Libraries folder that you use may me missing.
If you don't see your content after you update iTunes - Apple Support
Cheers