Your choice of backend and DB has nothing to do with the choice of your library or framework on the front-end.
I've always coded with what I know and it has worked for me - if you know PHP, go ahead and build your backend with PHP. If your data is relational and going to be suited for SQL, go for it by all means.
There are terminologies like MEAN and MERN going around, but I think that's just because someone who knew Mongo, Express, Angular and Node made it work together. Nothing's gonna stop you from using PHP, Laravel and MYSQL, so you can go ahead and call it a PLM stack.
Long story short, there's no single answer for the 'best' language on the backend to work with for react. 'Best' is not something that's tangible, everyone has their own definition. So, work with whatever language/framework you are comfortable with.
And, lastly, Welcome to Hashnode, Muhoho Jeremy. :D
Front-end Ninja