What should I do if I clicked on a phishing link on iphone?

From the scenario you described where you accidentally clicked on a phishing link on iphone, you rather have been a victim of a drive-by download attack that leads to installing -in most cases- adware or spyware but this attack can be even more dangerous depending on the malware that has been installed. This attack uses the browser vulnerabilities or the browser's plugins vulnerabilities using mainly malicious obfuscated JavaScript code.

The attack can be triggered passively by a simple visit to a given webpage as it happened for example in 2011 to Amnesty International's homepage where a lot of visitors got infected by simply reading articles on their homepage.
In another scenario, the attack needs the visitor to be active (which is the case you describe here): the visitor sees pop-up windows that a simple click on the OK, Cancel or even Exit (X) button will trigger the attack.