I’m looking for a service, that replicates the functionality of email aliases, but with phone numbers.
I’d imagine having one number (99999) which I then could use with suffixes like 99999-1, 99999-2, … etc for services like WhatsApp, telegram, 2FA, etc… if such thing even exists.
It depends a LOT on where you are. In the USA, Canada, and (I think) Mexico, such a thing is not possible, at least in any way that the services you mentioned will care.
It might be possible in places where phone numbers don’t have a fixed length, like (again, I think) Germany.