Yep, 80MB is big. That could be rejected by PHP itself. You should be able to configure these directives in PHP.ini as well. You need to look for POST_MAX_SIZE, UPLOAD_MAX_FILESIZE, MEMORY_LIMIT, and set the set_time_limit to increase the timeout. These all need to be larger than the file, and POST_MAX_SIZE should be > UPLOAD_MAX_FILESIZE (and MEMORY_LIMIT needs to be > POST_MAX_SIZE). And these are just the limitations with the PHP itself, I haven't a clue if phpmyadmin has any of its own.
All and all, why not just execute a command line call to the mysql dbms and provide it the file that way?
header('HTTP/1.1 420 Enhance Your Calm');