signal requires a phone number to sign up. a phone number could be used to trace your signal account back to you. so why do people, especially privacy enthusiasts and experts (like edward snowden), still use it and endorse it when it lacks anonymity in that sense? i get that people could use a voip number or something to sign up, but still.
Signal is a privacy first app. Do I wish it would not use a telephone number? Absolutely! But they never claim to be anonymous. This said with something like https://juicysms.com you can register signal and many other services with a number in the USA, the Netherlands or the UK (the Netherlands is the best option here)
If you look for an app what don’t need a telephone number check simplex or session. Perhaps something like the matrix protocol and element would be a great option too.