Azure DevOps PHP Application Store Local Files Question

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I have a PHP application that stores local files using the file_put_contents function. I have this PHP application running successfully on my own server that I manage. I am attempting to deploy it to the Azure DevOps PAAS. How do I create a directory that the PHP application can use to store files?

Currently, I use:

/var/www/html/php/tmpUploadDir

but it doesn't have to be in that location. I have attempted to create the tmpUploadDir directory by having it in my Git repository, but any files I save have a size of 0 bytes making me think I don't have permission to save it. I am flexible as to the location of the directory. Appreciate any assistance.