Is there a way to set a reminder or an event so when that event's time comes the iphone will say something like "your eventA is ready, keep in mind the traffic". Where that phrase is something i can control?
At the moment (up to and including iOS 12), you cannot have Siri speak to you based on an event (time/date, notification from app etc.). Only you can trigger Siri.
However, you could try a few things that may give you an approximation of what you want to do.
- Shortcuts: you could write a Shortcut in the Shortcuts app that has a time delay and then speaks the text you want. You cannot have this shortcut automatically invoked - you will have to trigger it - via your voice or your fingers - yourself.
- VoiceOver: you could enable VoiceOver to speak out your Reminders, Timers or Alarms.