1. Go to https://trends.builtwith.com/websitelist/PHP to see websites that use PHP
2. Focus on smaller to mid-size companies (large corporations likely have the tech team and contractors to cover almost of their needs)
3. (Optional) Search for each company on Linkedin and add managers with relevant roles (VIP of sales, project manager, marketing manager, etc.). The goal is to familiarize them with your name so they're more likely to open your email (step 5).
4. Find the email format of these companies with https://hunter.io/.
5. Reach out to the most senior person with a relevant role at each company with a personalized 1-on-1 email.
The key here is to review their website and business and share 2-3 ideas of what you can them build or fix (if there are any glaring issues or vulnerabilities). They may not necessarily use your ideas but the goal is stand out and help them understand how they can put your programming skills to use. Here's a template you can reference: https://artofemails.com/new-clients#developer
There are a lot of businesses out there whose teams don't have the capacity to build everything so they would be keen to have a reliable freelance programmer help them bring some features or projects out of backlog.