Yes, you need a phone number for Telegram. I doubt Telegram will be safe for much longer though, most of its operational infrastructure such as servers are based either in EU/NATO countries or in countries with close ties to Israel (eg: UAE). With Parler gone, I imagine either Telegram will be next to face some repercussions or they will crack down on nationalists and other controversial people on their platform to spare themselves (its already in some trouble for having a lot of jihadists on there).

There's going to be a huge crackdown on "alt-tech" and unless they can become autonomous in terms of infrastructure and hosting or manage to move to Chinese or Russian-based hosting that don't rely on any Western infrastructure or back-end services (which will be difficult for platforms which will have people a bunch of users crying about the CCP/ChiComs/Xi/Hong Kong), there's not really much that can be done except hopping between sites or attempting to stay on a certain platform for as long as possible. Apps and sites will be continually facing ultimatums to either be denied the ability to even host themselves or to join in censorship. If you really don't trust it, close your account on whatever site and leave.

(I'm not trying to be blackpilling, just realistic)