de0u Strong enough for what?
uppa9 More so keeping my data safe for a very long time
It's hard to say.
For example, if the question is "What if I put ultra-private data on an iPhone, turn it off, and lock it up a safe, will the data remain private in 50 years?" I would not want to predict that. Fifty years is a long time for somebody to find bugs in an obsolete iPhone.
If the iPhone is getting regular software updates, that's different (and presumably the ultra-private data will need to migrate to a new device every five years or so).
It also matters who wants the data. If it's a large state actor with powerful supercomputers, that's different than if it's a rural police detective. And if the state actor can torture you until you divulge your passphrase, that's entirely different.
It's hard to answer the question at all, and pretty impossible without a detailed threat model.