PHPC-837, there are complications with testing 32-bit builds for Linux in Evergreen. That said, most 32-bit users are likely on Windows environments, which will probably be easier to test in Evergreen (Perl and Python do this).
We would do well to advise users to use 64-bit environments, both for better test coverage and so they can avoid any complications with 64-bit integers (most recently addressed in
PHPC-1211). This note can be added to https://docs.mongodb.com/ecosystem/drivers/php/.