What aspect of this is specific to any embedded system? How would you accomplish your objective on conventional desktop or server hosts?
Really, your question is far too vague for anyone to provide a useful answer. Where, and under what context, is the SQL server running? Where and under what context is the PHP code running? How would you ordinarily communicate between an SQL server and your PHP code? Isn't sqlite a file-based system
? As such, I don't see how you can access it remotely, unless you use a file-read/file-modify/file-write system, which will have all sorts of perils if multiple users can concurrently access the database.