Riot.im uses the OLM encryption library (that is also used by XMPP OMEMO, see the OMEMO XEP). The OLM protocol is (I gather) very similar to the Signal protocol.
Riot is based on Matrix which is a decentralized protocol (you're not tied to one company), and it doesn't need your phone number.
Riot is based on Matrix which is a decentralized protocol (you're not tied to one company), and it doesn't need your phone number.