Version 3.3.1 or earlier typically includes PHP 5.6. You can find these on the official MAMP Downloads page by scrolling to the "Older Versions" section.
Once you restart the application, the version should appear in the Preferences > PHP dropdown menu. 3. Using MAMP PRO mamp php 5.6 download
The most reliable way to get PHP 5.6 is to download a legacy version of MAMP that originally included it. Version 3
For professional workflows, MAMP PRO provides a much easier interface for managing outdated languages. Downloads - MAMP & MAMP PRO mamp php 5.6 download