I assume it's a live site. You can encrypt the source. This product isn't free ($199) but maybe it helps you find something similar: https://www.sourceguardian.com/Geniun question.
Perhaps there's a free open source product...Our PHP encoder protects your PHP code by compiling the PHP source code into a binary bytecode format, which is then supplemented with an encryption layer. PHP 7.2 and PHP 7.3 are fully supported.