Clicking the Phoenician merchant notification, which appears along the right side of the screen, would redirect you to the city for which it is relevant (the city the Phoenician merchant has arrived at).
Currently, clicking the Phoenician merchant notification will open the merchant's trade screen, but not alter which city you were viewing before you clicked the notification.
As the 'Construction completed' notification redirects you to the city it applies to, so should the 'Phoenician merchant has arrived' notification. It would be a simple change to make but would, I think, be an improvement.
None.. it should be easy enough to understand without the need for visual aids.
This is simply an alteration which is already present in a way (construction complete notification redirection), so as far as I say it would not cause an imbalance, or be open to abuse.