Just to make sure I am getting your point, PHP cannot cause your trigger to fire - that is an instruction "hardwired" and internalized within the Mysql engine - that is my understanding anyway.
If your question is "how to you take the instructions in your triggers and have them run another way?" all I can suggest is that you
1 replicate the instructions in SQL statements
2 have PHP run those SQL statements when an event happens, and/or,
3 have cron call upon PHP to run the script against a time schedule