Phone numbers are an outdated idea, and shouldn't exist any more (and Signal is terrible for using them). You should have more privacy and have more control over your identity than what the legacy telecom setup allows. For example in most countries in Europe you can't get a phone number without a government ID tying it to your legal identity, and telecoms may be obliged to log your call metadata. Would you prefer e-mail as an open IP protocol, or a setup of traditional licensed postal operators that require government's permission to make an e-mail account for you?