I'm not sure what you are asking here.
If you have any doubts about whether or not PHP is running properly on your account, open Notepad and create a new file.
Save it on your desktop with any name.
Right click on the file on your desktop and rename it to test.php
Open it again in Notepad or any other plain text editor (not WordPad, Word etc) and paste this into it:
Save the file, upload to your web server and call the page in your browser.
The resulting page should display all the modules and other information about your account space.
Delete or rename the file on the server to test.not or something similar after you're done, since some of the information it returns can compromise the security of your web account.
Writing to files using PHP is done in a number of ways, but to begin with if you want your PHP program(s) to be able to write to a text file on the server it should be given write permissions - default file permissions are read. CHMOD the file to 666 or 775, depending on requirements, otherise your PHP can't write to the file.
Perhaps I've completely misunderstood your problem and in that case I apologise. If yuor test.php file with the above code runs OK then PHP is working on your account. If you get an error when calling the page you need to contact support to sort the issue out. Try the test first though.
It could help to know how you are uploading files, what you are editing them with, and possibly even some code to examine.