Wire (http://wire.com) has worked well on iOS for encrypted text/files/audio/video. Open-source client, no contact sharing neeeded. No phone number needed, you can register with email by using a desktop browser at http://app.wire.com, then logging into the mobile app. Group chat for text only. Timed/ephemeral messages for 1:1 text/files. Feature matrix, https://wire.com/privacy/. Could use more documentation (e.g. on retention of encrypted data) but a lot of questions are answered on Twitter or Github issues.