I've worked with Paul Jones in the past and he has actually modernized one of my own legacy PHP codebases. He wrote down his experiences and advice in "Moderniz

I've worked with Paul Jones in the past and he has actually modernized one of my own legacy PHP codebases. He wrote down his experiences and advice in "Modernizing Legacy Applications in PHP": https://leanpub.com/mlaphp https://leanpub.com/mlaphp It might be worth your time. (Edit: noir_lord also recommended the same book in this thread.)