phhttpd can be told to rotate its logs so that existing logs may be processed.
The --rotate argument to phhttpd_ctl tells phhttpd to rename the existing files to a unique name, open new files with the previously used names, then close the renamed logs and start using the newly created files. phhttpd_ctl will output the names of the newly created files which will be safe to use once the command exits.
The --reopen argument to phhttpd_ctl tells phhttpd to close the existing file logs and reopen the files with the filenames that were configured. This implies that an external entity has moved the files to new names and wants phhttpd to stop using them.