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…
soooo, honest opinions of discord users here: hows matrix nowadays? what are the other options?