Is there an API to obtain article information via DOI? Is there any API that allow to get article information (in JSON or BIBREF format) using article DOI? I need: article title, authors, journal name, year of publication, volume (number), page numbers.

Is there a script written in PHP?
You are looking for https://doi2bib.org . It shouldn't be very hard to extract the actual bibtex entry from the html you get from that page.

If you want to see how it works under the hood, take a look at the sources here: https://github.com/davidagraf/doi2bib2/ .