Sometimes not just "lean startup" type companies.
The place I'm thinking off that I know uses PHP for everything is a bricks and mortar retailer/manufacturer, I think last time I looked their revenue was ~£500m a year.
Their software was however awful in the worst ways :).
Basically the only two technologies I touch these days are rails and php. I'm not filtering out other tech stacks, these two are just absolutely dominant for this type of company.