Surprised no one else has chimed in with this yet - but what is your threat model? Are you conducting terrorist activities? Good luck. Are you wanting private messaging between you and your friends - it’s probably fine - definitely better than texting. I will temper this with just keep in mind anything you send to someone could be screenshot, their partner could see it etc. You need to figure out who your potential adversary is before deciding if a communication channel is “safe”. First ask yourself “safe from what?”.

depends on your threat model.

want to hide from advertising and general automated corpo creepness? sure. a reasonably hardened iphone will mostly do the trick.

want to hide from governments, three letter agencies or similar baddies who could simply order apple to give you the info? fuck no. apple unilaterally controls all the code that runs on it, and is itself subject to them.

theres the fact signal uses your phone number too…

Terms like “safe” and “private” are not binary.

Are the contents of your Signal conversations on an iPhone private with regard to mass surveillance conducted by governments and ISPs? Probably. Apple uses security and privacy as marketing points, and there are a whole lot of people looking for vulnerabilities in its products who are incentivized to disclose them (possibly with a delay for patches). Signal itself takes steps to prevent data leaks to less secure parts of the OS and other apps.

Would your conversations remain private in the face of a targeted attack against your device by a nation state willing to spend a significant amount of time and money when you’re using Signal on an iPhone that’s presumably used for purposes other than secure conversations with a small set of people you know? Almost certainly not.

iOS fails to include a libre software license text file, like AGPL. We do not control it, anti-libre software.

As long as you can trust Apple, sure

on an iPhone

Lol. No