The point is that they could. We are discussing honeypots here. They don't advertise the fact if they are.

Be the phone numbers hashed/encrypted or not they will still get your ip. They are not routing anybody's messages otherwise. Phone number is just more directly tied to a personal details, unless it's a burner, but with burners you lose the account if you need to log in. Also you can set your phone number public, so it probably can be seen by the signal servers at some point. And what about discovery through phone number and like the actual sending of the signal confirmation code? How is any that suppose to work if the servers don't know your actual phone number? And your anonymity trick only works if everybody you talk to does it, which they don't. If they want to profile you they can profile you directly or through the people you talk with. If the people you are trying to hide from don't care about getting message logs and just association with some group is punishable or can lead to punishment or death then tough luck.

And you miss the main point. practically speaking you cant self host a signal server, therefore you can't trust it fully (in a way 'fully' matters anyway). if you do it's unsupported and not recommended and you probably need a custom client to access it. That added with it being under American jurisdictions, and Signal starting as a spook project should really set off alarm bells.