It's safe to assume that any mobile phone OS will inevitably be targeted. There are always going to be unpatched and uncaught vulnerabilities, and the market for finding these vulns are very hot.
The bigger question is why do you think you'd be vulnerable to attack by a nation-state? If you are that prominent, you are screwed anyhow.
This article by Mickens is fairly accurate [0]
[0] - https://scholar.harvard.edu/files/mickens/files/thisworldofo...