Photo by David Alacaraz on Unsplash

Companies in Bay Area that use PHP:

23andMe — Mountain View

Adobe — San Jose and San Francisco

Apple — Cupertino

Baidu — Sunnyvale

BigCommerce — San Francisco

Buffer — San Francisco

Cisco — San Francisco

CNN — San Francisco

Credit Karma — San Francisco

Digg — San Francisco

eBay — San Jose

Etsy — San Francisco

Eventbrite — San Francisco

Facebook — Mountain View and San Franisco

Flikr — San Francisco

Google — Mountain View and San Francisco

HelloSign — San Francisco

Intuit — San Francisco

Oath (Yahoo!) — San Francisco

Salesforce — San Francisco

SanDisk — San Jose and Milpitas

Slack — San Francisco

Stitch Labs — San Francisco

Tumblr — San Francisco

Twilio — San Francisco

Weebly — San Francisco

Wikimedia — San Francisco

Workday — San Francisco and Dublin

For more info on Bay Area companies and their locations visit http://www.employbl.com/

If there are more companies to add let me know!