PHP 5.2 was removed from EasyApache due to its End of Life status. You can read about that here.
While downgrading to PHP 5.2 is not advised and is really kind of a terrible idea (given that 5.2 has been End of Life for years), cPanel provided some documentation on a way to downgrade PHP to this unsupported and end of life version here.
As outlined in that documentation you should run these commands on your server:
tar -C /var/cpanel/easy/apache/custom_opt_mods -xzf custom_opt_mod-PHP5217.tar.gz
Then recompile Apache using EasyApache. If you want no php except 5.2 then on the ‘PHP Version’ screen chose ‘none’, and continue. On step 4, the ‘Short Options List’ page you will see ‘PHP 5.2.17 support (no FastCGI)’ listed. Check that box and continue your EasyApache like normal.