Wire [1] is an app you could use across platforms for chat, voice calls and video calls (and even doodling). Sign up is using a phone number or an email address. It also has end-to-end encryption with multi-platform support and cross device sync (phone/desktop/laptop).

When I started using it a few months ago, the contacts discovery was a bit buggy, but it's worth a try. The feature set is quite rich.

[1]: https://www.wire.com