List of highly-regarded PHP style guides?

The PHP Standards Recommendations by the PHP Framework Interoperability Group are a good resource. AFAIK the standards are highly regarded. They attempt to be a collection and unification of what different frameworks have decided to use as their own standards.

I would say for basic PHP coding, especially PSR-1 and PSR-12 are well worth a read.

PSR-2′s purpose [was] to have a single style guide for PHP code that results in uniformly formatted shared code. [The PSR-12] specification extends, expands and replaces PSR-2, the coding style guide and requires adherence to PSR-1, the basic coding standard.

There are several accepted standard recommendations.

• PSR-1: Basic Coding Standard
• PSR-12: Extended Coding Style Guide
• All PSRs

I just use the PEAR coding standards.

http://pear.php.net/manual/en/standards.php

This is really for Codeigniter, but it's still PHP and an easy read and I like the styles used:

https://www.codeigniter.com/userguide2/general/styleguide.html